dt-bindings: Consolidate SRAM bindings from all vendors

SRAM bindings for various SoCs, using the mmio-sram genalloc
API, are spread over different places - per SoC vendor. Since all of
these are quite similar (they depend on mmio-sram) move them to a common
place.

Suggested-by: Rob Herring <robh+dt@kernel.org>
Signed-off-by: Krzysztof Kozlowski <k.kozlowski@samsung.com>
Cc: Heiko Stuebner <heiko@sntech.de>
Cc: Maxime Ripard <maxime.ripard@free-electrons.com>
Cc: Chen-Yu Tsai <wens@csie.org>
Cc: Kukjin Kim <kgene@kernel.org>
Acked-by: Maxime Ripard <maxime.ripard@free-electrons.com>
Acked-by: Heiko Stuebner <heiko@sntech.de>
Signed-off-by: Rob Herring <robh@kernel.org>