drm/i915: Add lmem_bar_size modparam

For testing purposes, support forcing the lmem_bar_size through a new
modparam. In CI we only have a limited number of configurations for DG2,
but we still need to be reasonably sure we get a usable device (also
verifying we report the correct values for things like
probed_cpu_visible_size etc) with all the potential lmem_bar sizes that
we might expect see in the wild.

v2: Update commit message and a minor modification.(Matt)

v3: Optimised lmem bar size code and modified code to resize
bar maximum upto lmem_size instead of maximum supported size.(Nirmoy)

v4: Optimised lmem bar size code.(Nirmoy)

Signed-off-by: Priyanka Dandamudi <priyanka.dandamudi@intel.com>
Cc: Matthew Auld <matthew.auld@intel.com>
Cc: Nirmoy Das <nirmoy.das@intel.com>
Reviewed-by: Nirmoy Das <nirmoy.das@intel.com>
Signed-off-by: Matthew Auld <matthew.auld@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20220713130209.2573233-3-priyanka.dandamudi@intel.com