msm: kgsl: Add generic functions to read efuse settings

Fuses are being increasingly used to provide SoC level configuration.
There is no common or generic way to read fuses so every leaf driver
is left to their own devices.

Add a set of generic functions to map and read efuse memory. Use
adreno_efuse_read_u32() to map/read/unmap a single address. If you
need to read more than one address at a time bracket the reads with
adreno_efuse_map() and adreno_efuse_unmap() to save multiple ioremaps
in a row.

Change-Id: Ic0dedbad951d323193e07e7a47ee8e7517738c9d
Signed-off-by: Jordan Crouse <jcrouse@codeaurora.org>