drm/radeon/kms: use defined constants for crtc/hpd count instead of hard-coded value 6

radeon_driver_irq_preinstall_kms and radeon_driver_irq_uninstall_kms
hard code the loop to 6 which happens to be the current maximum
number of crtcs and hpd pins; if one day an ASIC with more crtcs
(or hpd pins) comes out, this is a trouble waiting to happen.

introduce constants for maximum CRTC count, maximum HPD pins count
and maximum HDMI blocks count (per FIXME in radeon_irq structure)
and correct the loops in radeon_driver_irq_preinstall_kms and
radeon_driver_irq_uninstall_kms

v2: take care of goofs pointed out by Alex Deucher

Signed-off-by: Ilija Hadzic <ihadzic@research.bell-labs.com>
Reviewed-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Dave Airlie <airlied@redhat.com>