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Add support to generate rpm for MIPS and ARM.
To prevent confusion, we also removed build_script_arch
and use the deb/rpm arch directly as the build script argument.

Change-Id: Ifb44e4831e67a256e13bd02a1bfae09279448484
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2053783Reviewed-by: Thomas Anderson <thomasanderson@chromium.org>
Auto-Submit: Jiaxun Yang <jiaxun.yang@flygoat.com>
Commit-Queue: Lei Zhang <thestig@chromium.org>
Cr-Commit-Position: refs/heads/master@{#744913}