ARM: davinci: fix build failure with allnoconfig

allnoconfig build with just ARCH_DAVINCI enabled
fails because drivers/clk/davinci/* depends on
REGMAP being enabled.

Fix it by selecting REGMAP_MMIO when building in
DaVinci support.

Signed-off-by: Sekhar Nori <nsekhar@ti.com>
Reviewed-by: David Lechner <david@lechnology.com>
Signed-off-by: Arnd Bergmann <arnd@arndb.de>