[PATCH] Added backlight driver for Acer Aspire 4736

[Pradeep Subrahmanion]

Hi ,

  Brightness control was not  working on Acer Aspire 4736 using default ACPI interface.  acer-acpi also do not support 4730 series since it uses new WMI interface.
This driver adds brightness control by accessing the LBB PCI configuration register. This approach may also work on other laptops in 4730 series .But currently ,  it is only tested  for 
Aspire 4736.