intel_mid_powerbtn: use MSIC read/write instead of ipc_scu

In the 2.6.36 kernel we did not have the MSIC driver. Changed
all ipc_scu_reads/writes to use the MSIC driver and defines.
Added a fix from the 2.6.36 kernel where the SCU FW could send
a power button interrupt to the IA32 FW and the kernel was not
running yet. This resulted in the interrupt not getting cleared
and the power button was ignored. this fix just clears the
interrupt on start-up.

Signed-off-by: Michael Demeter <michael.demeter@intel.com>
Reviewed-by: Mika Westerberg <mika.westerberg@linux.intel.com>
Revert style-only changes. Remove unused variable. Fix comment style.]
Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Signed-off-by: Alan Cox <alan@linux.intel.com>
Signed-off-by: Matthew Garrett <mjg@redhat.com>