msm: spm: Ascertain and use the correct number of saw pmic data registers

Different SAW hardware can have a different number of pmic data registers.
Obtain the number of pmic data registers from the saw_id register. Use this
number to limit access to the available pmic data registers only, during
spm driver initialization.

Change-Id: I6b6f1928dea27057efa2d1efbb876249e6aca935
Signed-off-by: Karthik Parsha <kparsha@codeaurora.org>