msm: board-8930: Move board-8930-regulator.c to a PMIC specific file

Rename board-8930-regulator.c to board-8930-regulator-pm8038.c so
that regulator mappings can be made PMIC specific in order to
handle PM8038 vs PM8917 mapping at runtime.

Change-Id: I6b4bb822ff3a7e50b7b5f7f1a339459015e6908c
Signed-off-by: David Collins <collinsd@codeaurora.org>