input: touchscreen: Add support for kernel command line parsing

Add support for kernel command line parsing in atmel mxt touch
screen driver. This enables dynamic touch driver selection for
a given target.

Change-Id: I209542673cc89f89d90d4f0773165b4ebdbf12ae
Signed-off-by: Fei Mao <feim1@codeaurora.org>
Signed-off-by: Ritesh Kumar <riteshk@codeaurora.org>
Signed-off-by: Harigovindan P <harigovi@codeaurora.org>