msm: kgsl: Use nvmem to read the speed bin configuration

This patch uses the nvmem driver framework in the kernel to
read the speed bin efuse from qfprom. This was previously
read using raw register reads of ioremapped qfprom area.

Change-Id: I463471d35c9d02ab8e3ac3f8d961b1058698d430
Signed-off-by: Sharat Masetty <smasetty@codeaurora.org>