ARM: uniphier: consolidate SoC select menu

Currently, the supports for the following two ARMv7 SoC groups
are exclusive, because the boot ROM loads the SPL to a different
address:

 - LD4, sLD8                 (SPL is loaded at 0x00040000)
 - Pro4, Pro5, PXs2, LD6b    (SPL is loaded at 0x00100000)

This limitation exists only when CONFIG_SPL=y.

Instead of using crappy CONFIG options, checking SPL and SPL_TEXT_BASE
is cleaner.

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