i965/fs: Use regs_read/written for post-RA scheduling in calculate_deps

i965/fs: Use regs_read/written for post-RA scheduling in calculate_deps

Previously, we were assuming that everything read/wrote exactly 1 logical
GRF (1 in SIMD8 and 2 in SIMD16).  This isn't actually true.  In
particular, the PLN instruction reads 2 logical registers in one of the
components.  This commit changes post-RA scheduling to use regs_read and
regs_written instead so that we add enough dependencies.

Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=92770
Reviewed-by: Matt Turner <mattst88@gmail.com>
Reviewed-by: Connor Abbott <cwabbott0@gmail.com>