docs: qemu: add build instructions for QEMU_EFI.fd and rootfs.cpio.gz

This commit solves the limitation, "No build instructions for
QEMU_EFI.fd and rootfs-arm64.cpio.gz"

Document the steps to build them.

Change-Id: Ic6d895617cf71fe969f4aa9820dad25cc6182023
Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>

docs/plat/qemu.rst

@@ -20,11 +20,46 @@ provided as it's generated by QEMU.
 Current limitations:
 
 -  Only cold boot is supported
--  No build instructions for QEMU\_EFI.fd and rootfs-arm64.cpio.gz
 
-``QEMU_EFI.fd`` can be dowloaded from
+Getting non-TF images
+---------------------
+
+``QEMU_EFI.fd`` can be downloaded from
 http://snapshots.linaro.org/components/kernel/leg-virt-tianocore-edk2-upstream/latest/QEMU-KERNEL-AARCH64/RELEASE_GCC5/QEMU_EFI.fd
 
+or, can be built as follows:
+
+.. code:: shell
+
+    git clone https://github.com/tianocore/edk2.git
+    cd edk2
+    git submodule update --init
+    make -C BaseTools
+    source edksetup.sh
+    export GCC5_AARCH64_PREFIX=aarch64-linux-gnu-
+    build -a AARCH64 -t GCC5 -p ArmVirtPkg/ArmVirtQemuKernel.dsc
+
+````
+
+Then, you will get ``Build/ArmVirtQemuKernel-AARCH64/DEBUG_GCC5/FV/QEMU_EFI.fd``
+
+Please note you do not need to use GCC 5 in spite of the environment variable
+``GCC5_AARCH64_PREFIX``
+
+The rootfs can be built by using Buildroot as follows:
+
+.. code:: shell
+
+    git clone git://git.buildroot.net/buildroot.git
+    cd buildroot
+    make qemu_aarch64_virt_defconfig
+    utils/config -e BR2_TARGET_ROOTFS_CPIO
+    utils/config -e BR2_TARGET_ROOTFS_CPIO_GZIP
+    make olddefconfig
+    make
+
+Then, you will get ``output/images/rootfs.cpio.gz``.
+
 Booting via semi-hosting option
 -------------------------------
 
@@ -50,7 +85,7 @@ To start (QEMU v4.1.0):
     qemu-system-aarch64 -nographic -machine virt,secure=on -cpu cortex-a57  \
         -kernel Image                           \
         -append "console=ttyAMA0,38400 keep_bootcon root=/dev/vda2"   \
-        -initrd rootfs-arm64.cpio.gz -smp 2 -m 1024 -bios bl1.bin   \
+        -initrd rootfs.cpio.gz -smp 2 -m 1024 -bios bl1.bin   \
         -d unimp -semihosting-config enable,target=native
 
 Booting via flash based firmwares
@@ -99,5 +134,5 @@ To start (QEMU v2.6.0):
     qemu-system-aarch64 -nographic -machine virt,secure=on -cpu cortex-a57  \
         -kernel Image -no-acpi                     \
         -append 'console=ttyAMA0,38400 keep_bootcon root=/dev/vda2'  \
-        -initrd rootfs-arm64.cpio.gz -smp 2 -m 1024 -bios flash.bin   \
+        -initrd rootfs.cpio.gz -smp 2 -m 1024 -bios flash.bin   \
         -d unimp