aarch64: vp9 16bpp: Fix assembling with Xcode 6.2 and older

Properly use the b.eq form instead of the nonstandard form (which
both gas and newer clang accept though), and expand the register
lists that used a range (which the Xcode 6.2 clang, based on clang
3.5 svn, didn't support).

Signed-off-by: Martin Storsjö <martin@martin.st>