ARM: dig297: Define MACH_TYPE_OMAP3_CPS and CONFIG_MACH_TYPE

MACH_TYPE_OMAP3_CPS was dropped in the latest mach-types sync (47af6f61)
because it is not mainlined in Linux.

Signed-off-by: Luca Ceresoli <luca.ceresoli@comelit.it>
Cc: Sandeep Paulraj <s-paulraj@ti.com>
Cc: Albert Aribaud <albert.u.boot@aribaud.net>
Cc: Wolfgang Denk <wd@denx.de>
CC: Tom Rini <tom.rini@gmail.com>
Signed-off-by: Sandeep Paulraj <s-paulraj@ti.com>