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>

arch/c6x/kernel/devicetree.c

@@ -45,8 +45,3 @@ void __init early_init_dt_add_memory_arch(u64 base, u64 size)
 {
 	c6x_add_memory(base, size);
 }
-
-void * __init early_init_dt_alloc_memory_arch(u64 size, u64 align)
-{
-	return __va(memblock_alloc(size, align));
-}