ti: k3: abstract common fdt api for reserved mem fixups

ti: k3: abstract common fdt api for reserved mem fixups

The usage of fdt_fixup_reserved is repeated for ATF and OP-TEE for
multiple platforms, this patch creates a single fdt API for fixing up
the reserved-memory node with added error handling.

All k3 platforms already share a common tispl template which ensures
binaries are loaded as per the respective CONFIG_*_LOAD_ADDR. And the
provided new_size for the fixup is overridden by the size from fdt node
anyways. This allows for safe abstraction of the reserved memory fixups
for all current platforms.

fdt_fixup_reserved now abstracts the ATF and OP-TEE fixups by calling
the renamed static fdt_fixup_reserved_memory function with the required
parameters.

Signed-off-by: Anshul Dalal <anshuld@ti.com>