drm/i915: Parsing LFP brightness control from VBT

drm/i915: Parsing LFP brightness control from VBT

LFP brighness control from the VBT block 43 indicates which
controller is used for brightness.
LFP1 brightness control method:
Bit 7-4 = This field controller number of the brightnes controller.
0 = Controller 0
1 = Controller 1
2 = Controller 2
3 = Controller 3
Others = Reserved
Bits 3-0 = This field specifies the brightness control pin to be used on the
platform.
0 = PMIC pin is used for brightness control
1 = LPSS PWM is used for brightness control
2 = Display DDI is used for brightness control
3 = CABC method to control brightness
Others = Reserved

Adding the above fields in dev_priv->vbt and corresponding changes in
parse_backlight()

v2: Jani's review comments addressed
	- Move PWM definitions to intel_bios.h
	- Moving vbt_version to intel_vbt_data
	- Rename brightness to bl_ctrl_data
	- Logging just control_pin instead of string
	- Avoid adding vbt_version in dev_priv
	- Since only DDI option is available as of now, let control pin DDI
	affect dev_priv->vbt.backlight.present

v3: Jani's review comments addressed
	- Drop control_pin
	- Use bdb->version
	- set controller to 0 instead of using control pin define
	- check controller bounds
	- remove superfluous changes in intel_parse_bios

Signed-off-by: Deepak M <m.deepak@intel.com>
Signed-off-by: Vandana Kannan <vandana.kannan@intel.com>
Reviewed-by: Jani Nikula <jani.nikula@intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>