drm/i915/fbdev: Fix smem_start for LMEMBAR stolen objects

The "io" address of an object is its dma address minus the
region.start. Subtract the latter to make smem_start correct.
The current code happens to work for genuine LMEM objects
as LMEM region.start==0, but for LMEMBAR stolen objects
region.start!=0.

TODO: perhaps just set smem_start=0 always as our .fb_mmap()
implementation no longer depends on it? Need to double check
it's not needed for anything else...

Reviewed-by: Andrzej Hajda <andrzej.hajda@intel.com>
Tested-by: Paz Zcharya <pazz@chromium.org>
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20240202224340.30647-14-ville.syrjala@linux.intel.com

drm/i915: Use struct resource for memory region IO as well

mem->region is a struct resource, but mem->io_start and
mem->io_size are not for whatever reason. Let's unify this
and convert the io stuff into a struct resource as well.
Should make life a little less annoying when you don't have
juggle between two different approaches all the time.

Mostly done using cocci (with manual tweaks at all the
places where we mutate io_size by hand):
@@
struct intel_memory_region *M;
expression START, SIZE;
@@
- M->io_start = START;
- M->io_size = SIZE;
+ M->io = DEFINE_RES_MEM(START, SIZE);

@@
struct intel_memory_region *M;
@@
- M->io_start
+ M->io.start

@@
struct intel_memory_region M;
@@
- M.io_start
+ M.io.start

@@
expression M;
@@
- M->io_size
+ resource_size(&M->io)

@@
expression M;
@@
- M.io_size
+ resource_size(&M.io)

Reviewed-by: Andrzej Hajda <andrzej.hajda@intel.com>
Acked-by: Nirmoy Das <nirmoy.das@intel.com>
Tested-by: Paz Zcharya <pazz@chromium.org>
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20240202224340.30647-2-ville.syrjala@linux.intel.com

drm/i915/display: split i915 specific code from intel_fbdev

Split out code from intel_fbdev that can not be share between i915 and
xe. Create new i915 specific source/header file intel_fbdev_fb.[ch] which
contains this code.

Signed-off-by: Jouni Högander <jouni.hogander@intel.com>
Reviewed-by: Vinod Govindapillai <vinod.govindapillai@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20231115090719.3210079-2-jouni.hogander@intel.com