msm: mdss: debugfs: xlog: add support to dump registers by ranges

Current xlog dumps the entire registers ranges
mapped in memory. This entire range can be
reduced to only the meaningful offsets to help in
debugging and avoid overflows in the debug buffers.
This change adds support to only dump the registers
ranges specified.

Change-Id: Iecf7f5eaa909b0365ea599ae094c7f184c0ae8b8
Signed-off-by: Ingrid Gallardo <ingridg@codeaurora.org>