ARM: ep93xx: export ep93xx_chip_revision

ep93xx_chip_revision is used by the pata_ep93xx driver,
which can be a loadable module. Exporting the symbol
avoids a link error in this case.

Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Acked-by: Hartley Sweeten <hsweeten@visionengravers.com>
Cc: Ryan Mallon <rmallon@gmail.com>