[MIPS] Fix build issue for mips64el
[MIPS] Fix build issue for mips64el

Fixing build issue for mips64el by removing
WEBRTC_ARCH_MIPS64_FAMILY, and using WEBRTC_ARCH_MIPS_FAMILY
for both mipsel and mips64el.

BUG=undefined reference to webrtc::BlockDifference_SSE2_W32()
TEST=GYP_DEFINES="target_arch=mips64el mips_arch_variant=r2
     sysroot=<PATH_TO_SYSROOT>" webrtc/build/gyp_webrtc.py
     ninja -C out/Release
NOTRY=True

Review-Url: https://codereview.webrtc.org/2091433002
Cr-Original-Commit-Position: 972c6d2dc6dd5efdad1377c0d224e03eb8f276f7@{#13272}
Cr-Mirrored-From: https://chromium.googlesource.com/external/webrtc
Cr-Mirrored-Commit: 1fdcc28b25a257d460582e25956b43ef17ce03bd

jchavanton/webrtc,Alkalyne/webrtctrunk,Alkalyne/webrtctrunk,Alkalyne/webrtctrunk,Alkalyne/webrtctrunk,Alkalyne/webrtctrunk,jchavanton/webrtc,jchavanton/webrtc,Alkalyne/webrtctrunk,Alkalyne/webrtctrunk,jchavanton/webrtc,jchavanton/webrtc,jchavanton/webrtc,jchavanton/webrtc,Alkalyne/webrtctrunk