Add minimal riscv64 elf support to allow create_minidebuginfo on riscv64 binaries

This adds support for riscv64 elf files so that create_minidebuginfo
can be used strip riscv64 binaries.

Test: m create_minidebuginfo
Change-Id: I0cb0348d46ffb216af2f5c61701406504fae3b22
11 files changed