drm/i915/icp: Add Interrupt Support

This patch addresses Interrupts from south display engine (SDE).

ICP has two registers - SHOTPLUG_CTL_DDI and SHOTPLUG_CTL_TC.
Introduce these registers and their intended values.

Introduce icp_irq_handler().

The icp_irq_postinstall() takes care of
enabling all PCH interrupt sources, to unmask
them as needed with SDEIMR, as is done
done by ibx_irq_pre_postinstall() for earlier platforms.
We do not need to explicitly call the ibx_irq_pre_postinstall().

Also, while changing these,
s/CPT/PPT/CPT-CNP comment.

v2:
- remove redundant register defines.(Lucas)
- Change register names to be more consistent with
previous platforms (Lucas)

v3:
-Reorder bit defines to a more appropriate location.
 Change the comments. Confirm in the commit message that
 icp_irq_postinstall() need not go to
 ibx_irq_pre_postinstall() and ibx_irq_postinstall()
 as in earlier platforms. (Paulo)

Cc: Lucas De Marchi <lucas.de.marchi@gmail.com>
Cc: Paulo Zanoni <paulo.r.zanoni@intel.com>
Cc: Dhinakaran Pandiyan <dhinakaran.pandiyan@intel.com>
Cc: Ville Syrjala <ville.syrjala@linux.intel.com>
Reviewed-by: Lucas De Marchi <lucas.demarchi@intel.com>
Reviewed-by: Paulo Zanoni <paulo.r.zanoni@intel.com>
Signed-off-by: Anusha Srivatsa <anusha.srivatsa@intel.com>
[Paulo: coding style bikesheds and rebases].
Signed-off-by: Paulo Zanoni <paulo.r.zanoni@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/1530046343-30649-1-git-send-email-anusha.srivatsa@intel.com