qemu-arm64: Enable POSITION_INDEPENDENT

Now that PIE works when U-Boot is started from ROM, let's enable
CONFIG_POSITION_INDEPENDENT, which allows to load U-Boot also via
ARM Trusted-Firmware's fip.bin to DRAM, without tweaking the
configuration.

To get a writable initial stack, we need to keep the fixed initial
stack pointer, which points to DRAM in our case.

Signed-off-by: Andre Przywara <andre.przywara@arm.com>
Reviewed-by: Stephen Warren <swarren@nvidia.com>

arch/arm/Kconfig

@@ -22,6 +22,7 @@ config POSITION_INDEPENDENT
 
 config INIT_SP_RELATIVE
 	bool "Specify the early stack pointer relative to the .bss section"
+	default n if ARCH_QEMU
 	default y if POSITION_INDEPENDENT
 	help
 	  U-Boot typically uses a hard-coded value for the stack pointer

configs/qemu_arm64_defconfig

@@ -1,6 +1,7 @@
 CONFIG_ARM=y
 CONFIG_ARCH_QEMU=y
 CONFIG_NR_DRAM_BANKS=1
+CONFIG_POSITION_INDEPENDENT=y
 CONFIG_ENV_SIZE=0x40000
 CONFIG_ENV_SECT_SIZE=0x40000
 CONFIG_AHCI=y