r2dplus: use P1 area space for text base and PCI system memory

r2dplus: use P1 area space for text base and PCI system memory

While both options are acceptable use P1 area physical addresses
instead of external memory space of text base and PCI system memory
for unification purposes, all other supported superh boards have the
same selection.

This allows to easily ensure that CONFIG_SYS_TEXT_BASE is located
within available DRAM.

Signed-off-by: Vladimir Zapolskiy <vz@mleia.com>
Reviewed-by: Simon Glass <sjg@chromium.org>