payloads: Allow selecting UefiPayload on ARM64 platforms

Some ARM64 platforms (e.g., MT8195) are now able to compile
and run EDK2 (UefiPayload). As a result, we should allow selecting
PAYLOAD_TIANOCORE for ARM64 platforms.

TEST=show strings correctly.
1. make menuconfig
2. select Mainboard -> Vendor=Google, model=Cherry
3. select Payload -> Add a payload -> Tianocorepayload
4. make -j
5. build/cbfstool  build/coreboot.rom extract
   --name fallback/payload --file out.elf -m arm64
6. file out.elf # ELF 64-bit LSB executable, ARM aarch64
7. strings out.elf | grep tianocore # lots of tianocore stuff

Signed-off-by: Rex-BC Chen <rex-bc.chen@mediatek.com>
Change-Id: I10777a341d46240b91ceeeb1be26c33a0c5db839
Reviewed-on: https://review.coreboot.org/c/coreboot/+/58054
Reviewed-by: Rex-BC Chen <rex-bc.chen@mediatek.corp-partner.google.com>
Reviewed-by: Yu-Ping Wu <yupingso@google.com>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>

payloads/external/tianocore/Kconfig.name

@@ -1,6 +1,6 @@
 config PAYLOAD_TIANOCORE
 	bool "Tianocore payload"
-	depends on ARCH_X86
+	depends on ARCH_X86 || ARCH_ARM64
 	help
 	  Select this option if you want to build a coreboot image
 	  with a Tianocore payload. If you don't know what this is