ARM: uniphier: change stack pointer address for SPL

ARM: uniphier: change stack pointer address for SPL

No special reason for the current stack address 0x0ff08000.
Change it to 0x00100000 to simplify the init_page_table.

There are two types of SoCs in terms of the load address of SPL.

 [1] PH1-sLD3, PH1-LD4, PH1-sLD8
   SPL is loaded at 0x00040000-0x0004ffff
 [2] PH1-Pro4, PH1-Pro5, ProXstream2, PH1-LD6b
   SPL is loaded at 0x00100000-0x0010ffff

The new stack area (0x000f8000-0x00100000) should be safe for all the
cases.

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