ARM: l2c: clean up save/resume functions

Rename the pl310 save/resume functions to have a l2c310 prefix - this
is it's official name.  Use a local cached copy of the l2x0_base
virtual address, and also realise that many of the resume function
tails are the same as the enable functions, so make a call to the
enable function instead of duplicating that code.

Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>