intel/compiler: Add brw_get_compiler_config_value for disk cache

intel/compiler: Add brw_get_compiler_config_value for disk cache

During code review, Jason pointed out that:

2b3064c0731 "i965, anv: Use INTEL_DEBUG for disk_cache driver flags"

Didn't account for INTEL_SCALER_* environment variables.

To fix this, let the compiler return the disk_cache driver flags.

Another possible fix would be to pull the INTEL_SCALER_* into
INTEL_DEBUG bits, but as we are currently using 41 of 64 bits, I
didn't think it was a good use of 4 more of these bits. (5 since
INTEL_PRECISE_TRIG needs to be accounted for as well.)

Cc: Jason Ekstrand <jason@jlekstrand.net>
Signed-off-by: Jordan Justen <jordan.l.justen@intel.com>
Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>