Let's move handling and reset for gen11 display IRQs to their own
functions, similar to how we deal with GT interrupts.  This will make
the top-level functions a bit easier to read and potentially make things
easier to deal with in the future if new platforms wind up needing
different display handling logic.

Cc: Lucas De Marchi <lucas.demarchi@intel.com>
Signed-off-by: Matt Roper <matthew.d.roper@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20191202171608.3361125-1-matthew.d.roper@intel.comReviewed-by: Radhakrishna Sripada <radhakrishna.sripada@intel.com>