ARM: uniphier: shrink arrays of DDR-PHY parameters for LD20 SoC

The two arrays ddrphy_{op,ip}_dq_shift_val, occupy more than 3.8 KB
memory footprint, which is significant in SPL.

There are PHY parameters for 5 boards, but they are actually not
board specific, but SoC specific.  After all, we just need to have
2 patterns, for LD20 and LD21.  Also, the shift values are small
enough to become "short" type instead of "int".  This change will
save about 3 KB memory footprint.

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