ARM: update errata 430973 documentation to cover Cortex A8 r1p*

This errata covers all r1 variants of Cortex A8, it's not limited to
just r1p0..r1p2.  Update the documentation to reflect this.  The code
already applies the workaround to all r1p* A8 CPUs.

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