ARM: l2c: implement L2C-310 erratum 752271 in core L2C code

Rather than having SoCs work around L2C erratum themselves, move them
into core code.  This erratum affects the double linefill feature which
needs to be disabled for r3p0 to r3p1-50rel0.

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