memory: emif: Add Kconfig dependency for TI EMIF controller

Make TI_EMIF depends on ARCH_OMAP2PLUS to avoid build breaks on other
architectures. In future if other TI non OMAP socs start using it, the
dependency can be extended.

Signed-off-by: Santosh Shilimkar <santosh.shilimkar@ti.com>
Reported-by: Paul Gortmaker <paul.gortmaker@windriver.com>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>