x86, cleanup: remove cmdline_add_memmap_acpi

In kdump path, now we store all the 2nd kernel memory ranges in
memmap_p. We could use just cmdline_add_memmap() to add all types of
memory ranges to 2nd kernel cmdline.

So clean up here, merge cmdline_add_memmap_acpi() into
cmdline_add_memmap().

Signed-off-by: WANG Chao <chaowang@redhat.com>
Acked-by: Dave Young <dyoung@redhat.com>
Signed-off-by: Simon Horman <horms@verge.net.au>