i965: Create new program cache bo when clearing the program cache

i965: Create new program cache bo when clearing the program cache

When the disk shader cache CI testing was enabled, we started noticing
occasional failures on deqp test runs. (Mainly SNB, rarely HSW)

Before this change, when we cleared the (in memory) program cache we
reused the same bo. Since the disk shader cache quickly restores
programs, it appears that this would lead to overwrites of the older
program binaries in the in memory program cache that apparently were
still executing in some cases. If these programs were still executing,
this could cause a GPU hang.

This issue is probably not disk shader cache specific, but may have
been hidden due to the compiler taking time to recompile programs
after the cache was cleared.

v2:
 * Don't add `copy` param to brw_cache_new_bo (Ken)
 * Call from brw_program_cache_check_size (Ken)

Cc: Kenneth Graunke <kenneth@whitecape.org>
Cc: mesa-stable@lists.freedesktop.org
Signed-off-by: Jordan Justen <jordan.l.justen@intel.com>
Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>