staging: fsl-mc: Changed DPRC built-in portal's mc_io to be atomic

The DPRC built-in portal's mc_io is used to send commands to the MC
to program MSIs for MC objects. This is done by the
fsl_mc_msi_write_msg() callback, which is invoked by the generic MSI
layer with interrupts disabled. As a result, the mc_io used in
fsl_mc_msi_write_msg needs to be an atomic mc_io.

Signed-off-by: J. German Rivera <German.Rivera@freescale.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>