spmi: spmi-pmic-arb: add support for SPMI write corruption workaround

Add support for an AHB bus workaround which can be used to avoid
possible SPMI write transaction corruption on some platforms
which utilize PMIC arbiter version 5.  The workaround consists
of performing dummy reads of a PMIC arbiter register reached
via the AHB bus immediately before each register write during
an SPMI write transaction.

Change-Id: I13c7535f9fe823f9a2e74263ee5d5b674e0c1fbc
Signed-off-by: David Collins <collinsd@codeaurora.org>