pinctrl: single: fix compile warnings with PHYS_64BIT on 32bit

pinctrl-single uses fdt_addr_t and phys_addr_t inconsistently, but both
are wrong to be passed to readb() etc., which expect a pointer or
pointer-sized integer. Change the driver to use
dev_read_addr_size_index_ptr(), so we consistently deal with void*
(except for the sandbox case and single_get_pin_muxing()).

Signed-off-by: Matthias Schiffer <matthias.schiffer@ew.tq-group.com>
Reviewed-by: Simon Glass <sjg@chromium.org>
Add missing mapmem.h header:
Signed-off-by: Simon Glass <sjg@chromium.org>