C6X: EMIF - External Memory Interface

Several SoC parts provide a simple bridge to support external memory mapped
devices. This code probes the device tree for an EMIF node and sets up the
bridge registers if such a node is found. Beyond initial set up, there is no
further need to access the bridge control registers. External devices on the
bus are accessed through their MMIO registers using suitable drivers. The
bridge hardware does provide for timeout and other error interrupts, but these
are not yet supported.

Signed-off-by: Mark Salter <msalter@redhat.com>
Signed-off-by: Aurelien Jacquiot <a-jacquiot@ti.com>
Acked-by: Arnd Bergmann <arnd@arndb.de>