msm: mdm: change the way callbacks are passed to common code.

The common code now keeps a reference to a static struct containing
pointers to the callback functions instead of the individual function
pointers themselves. This is more in keeping with the normal way ops
are passed in the kernel.

Change-Id: I64fce3214d22071421be46cdd82654bbc6bccc1d
Signed-off-by: Joel King <joelking@codeaurora.org>