ARM: prima2: remove duplicate v7_invalidate_l1

Patch c08e20d "arm: Add v7_invalidate_l1 to cache-v7.S" added
a generic version of this function and removed all platform
specific versions, while 4898de3 "ARM: PRIMA2: add new SiRFmarco
SMP SoC infrastructures" added another one, leading to a link
error. I verified that the two are identical, so we can
just remove the one in mach-prima2.

Signed-off-by: Arnd Bergmann <arnd@arndb.de>