memblock: use separate iterators for memory and reserved regions

for_each_memblock() is used to iterate over memblock.memory in a few
places that use data from memblock_region rather than the memory ranges.

Introduce separate for_each_mem_region() and
for_each_reserved_mem_region() to improve encapsulation of memblock
internals from its users.

Signed-off-by: Mike Rapoport <rppt@linux.ibm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Reviewed-by: Baoquan He <bhe@redhat.com>
Acked-by: Ingo Molnar <mingo@kernel.org>			[x86]
Acked-by: Thomas Bogendoerfer <tsbogend@alpha.franken.de>	[MIPS]
Acked-by: Miguel Ojeda <miguel.ojeda.sandonis@gmail.com>	[.clang-format]
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Christoph Hellwig <hch@lst.de>
Cc: Daniel Axtens <dja@axtens.net>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: Emil Renner Berthing <kernel@esmil.dk>
Cc: H...