ARM: multi_v7_defconfig: enable SDHCI_BCM_KONA and MMC_BLOCK_MINORS=16

Enable MMC/SD on the Broadcom mobile platforms, and increase the block
minors from the default 8 to 16 (since the Broadcom board by default
has root on the 8th partition).

Signed-off-by: Olof Johansson <olof@lixom.net>
Cc: stable@vger.kernel.org # v3.12