drm/xe/hwmon: Add support to manage power limits though mailbox

drm/xe/hwmon: Add support to manage power limits though mailbox

Add support to manage power limits using pcode mailbox commands
for supported platforms.

v2:
 - Address review comments. (Badal)
 - Use mailbox commands instead of registers to manage power limits
   for BMG.
 - Clamp the maximum power limit to GPU firmware default value.

v3:
 - Clamp power limit in write also for platforms with mailbox support.

v4:
 - Remove unnecessary debug prints. (Badal)

v5:
 - Update description of variable pl1_on_boot to fix kernel-doc error.

v6:
 - Improve commit message, refer to BIOS as GPU firmware.
 - Change macro READ_PL_FROM_BIOS to READ_PL_FROM_FW.
 - Rectify drm_warn to drm_info.

Signed-off-by: Karthik Poosa <karthik.poosa@intel.com>
Fixes: e90f7a58e659 ("drm/xe/hwmon: Add HWMON support for BMG")
Reviewed-by: Badal Nilawar <badal.nilawar@intel.com>
Link: https://lore.kernel.org/r/20250529163458.2354509-2-karthik.poosa@intel.com
Signed-off-by: Rodrigo Vivi <rodrigo.vivi@intel.com>