ARM: dts: dra7: Add ocmcram nodes

ARM: dts: dra7: Add ocmcram nodes

Add all ocmcram nodes to dra7.dtsi using the generic mmio-sram driver.
DRA7xx and AM57xx families of SoCs can contain three ocmcram regions of
SRAM, one of 512kb and also an optional two additional of 1Mb each. Mark
the two additional 1MB regions of SRAM as disabled as only ocmcmram1 is
on all variants of the SoCs, then depending on which specific variant
is in use the ocmcram2 and ocmcram3 nodes can be enabled in the board
dts file if the data manual for that part number indicates the ocmcram
region is available.

Signed-off-by: Dave Gerlach <d-gerlach@ti.com>
Reviewed-by: Andreas Dannenberg <dannenberg@ti.com>
Signed-off-by: Tony Lindgren <tony@atomide.com>