srec: rename aarch64 target to arm64

Rename aarch64 build targets to arm64.  The gcc toolchain is still
aarch64.

Change-Id: Ia92d8a50824e5329cf00fd6f4f92eae112b7f3a3
Merge "srec: rename aarch64 target to arm64"
[MIPS64] Support mips64

Change-Id: Ib32fb0d4b6d3eb0fcef7e59da99c13217a530b7c
Merge "[MIPS64] Support mips64"