CM4000: fix missing RAM definitions for OpenGear boards

The OpenGear boards CM4008, CM4116 and CM4148 need their DRAM base
and RAM stack base addresses defined.

Fixes:

board.c: In function ‘__dram_init_banksize’:
board.c:227: error: ‘CONFIG_SYS_SDRAM_BASE’ undeclared (first use in this function)
board.c:227: error: (Each undeclared identifier is reported only once
board.c:227: error: for each function it appears in.)
board.c: In function ‘board_init_f’:
board.c:270: error: ‘CONFIG_SYS_INIT_SP_ADDR’ undeclared (first use in this function)
board.c:303: error: ‘CONFIG_SYS_SDRAM_BASE’ undeclared (first use in this function)

Signed-off-by: Greg Ungerer <greg.ungerer@opengear.com>