drm/i915/lmem: debugfs for LMEM details

Debugfs i915_gem_object is extended to enable the IGTs to
detect the LMEM's availability and the total size of LMEM.

v2: READ_ONCE is used [Chris]
v3: %pa is used for printing the resource [Chris]
v4: All regions' details added to debugfs [Chris]
v5: Macro for_each_mem_region added
    name is initialized at region init [Chris]

Signed-off-by: Lukasz Fiedorowicz <lukasz.fiedorowicz@intel.com>
Signed-off-by: Matthew Auld <matthew.auld@intel.com>
Signed-off-by: Stuart Summers <stuart.summers@intel.com>
Signed-off-by: Ramalingam C <ramalingam.c@intel.com>
Cc: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Link: https://patchwork.freedesktop.org/patch/msgid/20191227133748.4330-1-ramalingam.c@intel.com