isl: Drop WaDisableSamplerL2BypassForTextureCompressedFormats on Gen11

Gen11 doesn't require us to bypass the L2 cache for BC* images anymore.

The documentation is a bit hard to follow on this point, but the Windows driver clearly only applies this workaround on Gen9, and their commit history indicates that this was an intentional change to drop the workaround for Gen11+.