This updates the GPU headers to latest from mesa, using gen_header.py
(which is used to generate headers at bulid time for mesa), rather than
headergen2 (which doesn't have proper support for A6XX vs A7XX register
variants).

Mostly just uninteresting churn, but there are a couple spots in a7xx
paths which update REG_A6XX_foo to REG_A7XX_foo for registers which are
a7xx specific.

Cc: Connor Abbott <cwabbott0@gmail.com>
Signed-off-by: Rob Clark <robdclark@chromium.org>
Acked-by: Konrad Dybcio <konrad.dybcio@linaro.org>
Patchwork: https://patchwork.freedesktop.org/patch/574880/