asm_macros: set the default assembly code alignment to 4 byte

Assembly routines are usually defined by using "func" and "endfunc":

    func foo
      ...
    endfunc foo

Currently, the "func" macro does not specify ".align" directive
by default.  It causes unaligned instruction under some circumstances.

As far as I tested, this problem happens for GCC 5 or older.  It did
not happen for GCC 6 or newer.  Taking into account that GCC 4.x / 5.x
is still used, make sure that assembly code is at least 4 byte aligned.

[ How to reproduce the problem ]

For example, use GCC 5.3 downloaded from Linaro:
http://releases.linaro.org/components/toolchain/binaries/5.3-2016.05/
aarch64-linux-gnu/gcc-linaro-5.3.1-2016.05-x86_64_aarch64-linux-gnu.tar.xz

Expand mbedtls-2.4.2 to the current directory.

Try the following:

  $ git log --oneline -1
  77544efb

 Merge pull request #1071 from jeenu-arm/syntax-fix
  $ aarch64-linux-gnu-gcc --version | head -1
  aarch64-linux-gnu-gcc (Linaro GCC 5.3-2016.05) 5.3.1 20160412
  $ make CROSS_COMPILE=aarch64-linux-gnu- PLAT=uniphier \
    TRUSTED_BOARD_BOOT=1 MBEDTLS_DIR=mbedtls-2.4.2
    ( snip build log )
  $ aarch64-linux-gnu-nm build/uniphier/release/bl1/bl1.elf | grep handler
  00000000800088f4 T bl1_fwu_smc_handler
  00000000800084c8 T bl1_smc_handler
  000000008000a6e0 t _panic_handler
  000000008000a8e0 W plat_error_handler
  000000008000a8e8 W plat_panic_handler
  000000008000a8d8 W plat_reset_handler
  000000008000a39f T reset_handler
  000000008000a367 t smc_handler
  000000008000a2ef t smc_handler64

You will notice "smc_handler64", "reset_handler", etc. are not properly
aligned.
Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>

include/common/asm_macros_common.S

@@ -12,11 +12,12 @@
 	 * to enable elimination of unused code during linking. It also adds
 	 * basic debug information to enable call stack printing most of the
 	 * time. The optional _align parameter can be used to force a
-	 * non-standard alignment (indicated in powers of 2). Do *not* try to
-	 * use a raw .align directive. Since func switches to a new section,
-	 * this would not have the desired effect.
+	 * non-standard alignment (indicated in powers of 2). The default is
+	 * _align=2 because both Aarch32 and Aarch64 instructions must be
+	 * word aligned. Do *not* try to use a raw .align directive. Since func
+	 * switches to a new section, this would not have the desired effect.
 	 */
-	.macro func _name, _align=-1
+	.macro func _name, _align=2
 	/*
 	 * Add Call Frame Information entry in the .debug_frame section for
 	 * debugger consumption. This enables callstack printing in debuggers.
@@ -36,9 +37,7 @@
 	 * .debug_frame
 	 */
 	.cfi_startproc
-	.if (\_align) != -1
-		.align \_align
-	.endif
+	.align \_align
 	\_name:
 	.endm