ARM: uniphier: fix ROM boot mode for PH1-sLD3

Commit 4b50369f ("ARM: uniphier: create early page table at
run-time") broke the ROM boot mode for PH1-sLD3 SoC, because the
run-time page table creation requires the outer cache register
access but the page table in the sLD3 Boot ROM does not straight-map
virtual/physical addresses.

The idea here is to check the current page table to determine if
it is a straight map table.  If not, adjust the outer cache register
base.

Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>