i965/fs: fix copy propagation of partially invalidated entries

i965/fs: fix copy propagation of partially invalidated entries

We were not invalidating entries with a src that reads more than one register
when we find writes that overwrite any register read by entry->src after
the first. This leads to incorrect copy propagation because we re-use
entries from the ACP that have been partially invalidated. Same thing for
entries with a dst that writes to more than one register.

v2 (Sam):
- Improve code by defining regions_overlap() and using it instead of a
loop (Curro).

Reviewed-by: Francisco Jerez <currojerez@riseup.net>
Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>