The internal cp interrupts need to be enabled and
disabled at specific times in order clockgating to
work properly.  This patch changes the handling
of the CP_INT_CNTL register to respect the current
state of the internal CP interrupts when making
changes to the other interrupts in CP_INT_CNTL.
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>