Introduce console_uninit() API in ARM Trusted Firmware

Allowing console base address to be set to NULL conveniently
allows console driver to ignore further invocations to console_putc()
and console_getc(). This patch adds `console_uninit()` API to the
console driver which sets console base address as NULL. The BL images can
invoke this API to finish the use of console and ignore any further
invocations to print to the console.

Change-Id: I00a1762b3e0b7c55f2be2f9c4c9bee3967189dde

drivers/console/console.S

@@ -30,6 +30,7 @@
 #include <asm_macros.S>
 
 	.globl	console_init
+	.globl	console_uninit
 	.globl	console_putc
 	.globl	console_getc
 
@@ -66,6 +67,20 @@ init_fail:
 	ret
 endfunc console_init
 
+	/* -----------------------------------------------
+	 * void console_uninit(void)
+	 * Function to finish the use of console driver.
+	 * It sets the console_base as NULL so that any
+	 * further invocation of `console_putc` or
+	 * `console_getc` APIs would return error.
+	 * -----------------------------------------------
+	 */
+func console_uninit
+	mov	x0, #0
+	adrp	x3, console_base
+	str	x0, [x3, :lo12:console_base]
+endfunc console_uninit
+
 	/* ---------------------------------------------
 	 * int console_putc(int c)
 	 * Function to output a character over the

include/drivers/console.h

@@ -35,6 +35,7 @@
 
 int console_init(uintptr_t base_addr,
 		unsigned int uart_clk, unsigned int baud_rate);
+void console_uninit(void);
 int console_putc(int c);
 int console_getc(void);