msm: regmap: configure REGMAP debugfs write optional

Currently, REGMAP debugfs write is always permitted, which
poses a risk of some unexpected PMIC setting. Make
REGMAP_ALLOW_WRITE_DEBUGFS configurable so debugfs write
can be disabled when not desired.

CRs-Fixed: 2002923
Change-Id: I5cbc5f118c97230dc6ef46cb2363a06823cb6c7a
Signed-off-by: Harry Yang <harryy@codeaurora.org>