Expose display revision

According to customer requirements.

Display Driver needs to read IC's RDDID registers to expose LCM revision.

To avoid PCBA's file node get influences,

I create another file node to expose LCM revision.

User can type "cat /proc/lcm_revision" to exposes LCM revision.

Change-Id: I64d7ea1a03ddf371a5468962fe0e5c3d9caa3fc7