MIPS: Loongson64: Do not override watch and ejtag feature

Do not override ejtag feature to 0 as Loongson 3A1000+ do have ejtag.
For watch, as KVM emulated CPU doesn't have watch feature, we should
not enable it unconditionally.

Signed-off-by: Jiaxun Yang <jiaxun.yang@flygoat.com>
Reviewed-by: Huacai Chen <chenhc@lemote.com>
Signed-off-by: Thomas Bogendoerfer <tsbogend@alpha.franken.de>