of: reserved_mem: switch to ops based OF_DECLARE()

of: reserved_mem: switch to ops based OF_DECLARE()

Move init function from OF_DECLARE() argument to the given reserved
memory region ops structure and then pass that structure to the
OF_DECLARE() initializer. This node_init callback is mandatory for the
reserved mem driver. Such change makes it possible in the future to add
more functions called by the generic code before given memory region is
initialized and rmem object is created.

Signed-off-by: Marek Szyprowski <m.szyprowski@samsung.com>
Link: https://patch.msgid.link/20260325090023.3175348-4-m.szyprowski@samsung.com
Signed-off-by: Rob Herring (Arm) <robh@kernel.org>