ARM: 6676/1: Correct the cpu_architecture() function for ARMv7

If ID_MMFR0[3:0] >= 3, the architecture version is ARMv7. The code was
currently only testing for ID_MMFR0[3:0] == 3.

Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>