MIPS: p5600: Discard UCA config selection

Commit 2a598436 ("MIPS: Drop CPU_SUPPORTS_UNCACHED_ACCELERATED")
removed UCA config, but left the selection unused, delete it.

Signed-off-by: Jinyang He <hejinyang@loongson.cn>
Signed-off-by: Thomas Bogendoerfer <tsbogend@alpha.franken.de>