[Intel-gfx] Ivybridge hang fixes respun

[Kenneth Graunke]

These fix many GPU hangs for Eugeni, though not on my machine for some
reason.

Oddly, the register writes to UCGCTL2 and SQ_CHICKEN_MBCUNIT_CONFIG stick,
but the writes to L3_CHICKEN_MODE, L3CNTLREG1, and COMMON_SLICE_CHICKEN1
don't seem to take effect.  Currently no theories why.

Manually writing these values with intel_reg_write /does/ fix the hangs
for me.

I'm fine with these going to -fixes.  They seem to help some people, and
I highly doubt they'll make anything worse.  It'd be nice to understand
why the register writes aren't sticking, though...