add support for the am335x based shc board.

UART: 0-2 and 4
DRAM: 512 MiB
MMC:  OMAP SD/MMC: 0 @ 26 MHz
      OMAP SD/MMC: 1 @ 26 MHz
I2C:  at24 eeprom, pcf8563
USB:  USB1 (host)
Signed-off-by: Heiko Schocher <hs@denx.de>
Signed-off-by: Tony Lindgren <tony@atomide.com>