radeonsi: fix CMASK and HTILE allocation on Tahiti

radeonsi: fix CMASK and HTILE allocation on Tahiti

Tahiti has 12 tile pipes, but P8 pipe config.

It looks like there is no way to get the pipe config except for reading
GB_TILE_MODE. The TILING_CONFIG ioctl doesn't return more than 8 pipes,
so we can't use that for Hawaii.

This fixes a regression caused by 9b046474c95f15338d4c748df9b62871bba6f36f
on Tahiti.

v2: add an assertion and print an error on failure

Cc: mesa-stable@lists.freedesktop.org
Reviewed-by: Michel Dänzer <michel.daenzer@amd.com>