LoongArch: Check TIF_LOAD_WATCH to enable user space watchpoint

Currently, there are some places to set CSR.PRMD.PWE, the first one is
in hw_breakpoint_thread_switch() to enable user space singlestep via
checking TIF_SINGLESTEP, the second one is in hw_breakpoint_control() to
enable user space watchpoint. For the latter case, it should also check
TIF_LOAD_WATCH to make the logic correct and clear.

Fixes: c8e57ab0 ("LoongArch: Trigger user-space watchpoints correctly")
Signed-off-by: Tiezhu Yang <yangtiezhu@loongson.cn>
Signed-off-by: Huacai Chen <chenhuacai@loongson.cn>