drm/msm: a6xx: Fix gx_is_on check for a7x family

drm/msm: a6xx: Fix gx_is_on check for a7x family

Bitfield definition for REG_A6XX_GMU_SPTPRAC_PWR_CLK_STATUS register is
different in A7XX family. Check the correct bits to see if GX is
collapsed on A7XX series.

Fixes: af66706accdf ("drm/msm/a6xx: Add skeleton A7xx support")
Signed-off-by: Akhil P Oommen <akhilpo@oss.qualcomm.com>
Reviewed-by: Konrad Dybcio <konrad.dybcio@oss.qualcomm.com>
Patchwork: https://patchwork.freedesktop.org/patch/673358/
Signed-off-by: Rob Clark <robin.clark@oss.qualcomm.com>