msm: kgsl: Change __cpuc_flush_kern_all() to flush_cache_all()

The two above mentioned calls both perform the same function of
flushing the entire cache. flush_cache_all() is present on
multiple platforms, so switch to it.

Change-Id: If9996a44620108d09694df004073d6b825a76dc4
Signed-off-by: Shrenuj Bansal <shrenujb@codeaurora.org>