ARM: OMAP2+: Add function for configuring GPMC settings

ARM: OMAP2+: Add function for configuring GPMC settings

The GPMC has various different configuration options such as bus-width,
synchronous or asychronous mode selection, burst mode options etc.
Currently, there is no common function for configuring these options and
various devices set these options by either programming the GPMC CONFIG1
register directly or by calling gpmc_cs_configure() to set some of the
options.

Add a new function for configuring all of the GPMC options. Having a common
function for configuring this options will simplify code and ease the
migration to device-tree.

Also add a new capability flag to detect devices that support the
address-address-data multiplexing mode.

Signed-off-by: Jon Hunter <jon-hunter@ti.com>
Tested-by: Ezequiel Garcia <ezequiel.garcia@free-electrons.com>