add armv7 builds

This is the usual slew, plus
   - .vfpv2      --> a non-NEON build
   - .neon-vfpv4 --> a build with NEON and F16 conversion

The default is equivalent to .neon-vfpv3.

Change-Id: I3723bfab44f1a1388ed0f0682f00972728fd0431
Reviewed-on: https://skia-review.googlesource.com/97081
Reviewed-by: Brian Osman <brianosman@google.com>
9 files changed