of: consolidate definition of early_init_dt_alloc_memory_arch()

Most architectures use the same implementation. Collapse the common ones
into a single weak function that can be overridden.

Signed-off-by: Grant Likely <grant.likely@linaro.org>
Git-commit: a1727da599ad030ccaf4073473fd235c8ee28219
Git-repo: git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git


Signed-off-by: Ian Maund <imaund@codeaurora.org>