drm/i915/gtt: reduce overzealous alignment constraints for GGTT

Currently this will enforce both 2M alignment and padding for any LMEM
pages inserted into the GGTT. However, this was only meant to be applied
to the compact-pt layout with the ppGTT. For the GGTT we can reduce the
alignment and padding to 64K.

Bspec: 45015
Fixes: 87bd701e

 ("drm/i915: enforce min GTT alignment for discrete cards")
Signed-off-by: Matthew Auld <matthew.auld@intel.com>
Cc: Thomas Hellström <thomas.hellstrom@linux.intel.com>
Cc: Robert Beckett <bob.beckett@collabora.com>
Cc: Ramalingam C <ramalingam.c@intel.com>
Reviewed-by: Thomas Hellström <thomas.hellstrom@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20220303100229.839282-1-matthew.auld@intel.com