Switch armv7 setting to arm_version==7 in v8 gyp files

BUG=chromium:234135
LOG=Y
R=jkummerow@chromium.org

Review URL: https://codereview.chromium.org/98543008

Patch from Mostyn Bramley-Moore <mostynb@opera.com>.

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@18297 ce2b1a6d-e550-0410-aec6-3dcde31c8c00