msm: hotplug: Change the pen variable in one place

Other WFI based hotplug implementations set the pen variable to
-1 in C code and do the appropriate flushing operations in one
location. They also don't try to invalidate the cache on a
spurious wakeup and report how many spurious wakeups there were.
Let's do the same in our code so that we can remove our
dependence on the dmac_{inv,flush}_range() functions (which are
no longer upstream) and easily report spurious wakeups to the
kernel logs.

This does delay the time we set the pen back to its default
value, but that doesn't actually matter because generic ARM
hotplug code already waits for a completion before continuing.

Change-Id: Ic36fbf744fe8abeda20ad9859a207b5e37c5e63c
Signed-off-by: Stephen Boyd <sboyd@codeaurora.org>