msm: msi: add hooks for MSI enable/disable

There are cases where MSI IRQ mask/unmask does not
correctly disable the source IRQ. Add enable and
disable hooks to handle these cases.

Change-Id: Ifdad14fc7af3b11ad1cdd54edcf991349ee83733
Signed-off-by: Tony Truong <truong@codeaurora.org>