dm: core: Add dev_get_addr_size_index() to retrieve addr and size

dm: core: Add dev_get_addr_size_index() to retrieve addr and size

The currently available functions accessing the 'reg' property of a
device only retrieve the address. Sometimes its also necessary to
retrieve the size described by the 'reg' property. This patch adds
the new function dev_get_addr_size_index() which retrieves both,
the address and the size described by the 'reg' property.

Signed-off-by: Stefan Roese <sr@denx.de>
Cc: Simon Glass <sjg@chromium.org>
Acked-by: Simon Glass <sjg@chromium.org>