ARM: davinci_all_defconfig: build MMC into kernel

This changes the davinci default configuration to build the davinci
MMC driver into the kernel. This allows booting from an SD card without
requiring an initrd containing the kernel module.

Signed-off-by: David Lechner <david@lechnology.com>
[nsekhar@ti.com: minor commit message adjustments]
Signed-off-by: Sekhar Nori <nsekhar@ti.com>