msm: kgsl: Remove SPTP headswitch controls for new targets

Starting from sdm855, the SPTPRAC headswitch is removed
from the GPU. Add a check to functions that touch the
relevant registers to make sure we do not proceed if
we are not a615 or a630.

Change-Id: I84c3cf615b2cac0b56a303603afb29a91caaff1b
Signed-off-by: Kyle Piefer <kpiefer@codeaurora.org>