board: qemu-arm: select CONFIG_HAS_CUSTOM_SYS_INIT_SP_ADDR

qemu_arm64_defconfig with CONFIG_HAS_CUSTOM_SYS_INIT_SP_ADDR=n leads to a
build error:

    arch/arm/lib/crt0_64.S:85:
    Error: constant expression expected at operand 2 --
    `ldr x0,=((CFG_SYS_INIT_RAM_ADDR+CFG_SYS_INIT_RAM_SIZE-480))'

We do not define CFG_SYS_INIT_RAM_ADDR and CFG_SYS_INIT_RAM_SIZE for QEMU.

Signed-off-by: Heinrich Schuchardt <heinrich.schuchardt@canonical.com>
Acked-by: Ilias Apalodimas <ilias.apalodimas@linaro.org>
diff --git a/board/emulation/qemu-arm/Kconfig b/board/emulation/qemu-arm/Kconfig
index e21c135..80ab9d8 100644
--- a/board/emulation/qemu-arm/Kconfig
+++ b/board/emulation/qemu-arm/Kconfig
@@ -5,6 +5,7 @@
 
 config BOARD_SPECIFIC_OPTIONS # dummy
 	def_bool y
+	select HAS_CUSTOM_SYS_INIT_SP_ADDR
 	select QFW if ACPI
 	select QFW_MMIO if CMD_QFW
 	imply VIRTIO_MMIO