target/loongarch: Guard BCEQZ/BCNEZ instructions with FP feature

target/loongarch: Guard BCEQZ/BCNEZ instructions with FP feature

The BCEQZ and BCNEZ instructions depend on access to condition codes
from floating-point comparisons. Previously, these instructions were
unconditionally enabled for 64-bit targets.

This patch updates their translation to be gated under the `FP` feature
flag instead, ensuring they are only available when the floating-point
unit is present.

This improves correctness for CPUs lacking floating-point support.

Signed-off-by: WANG Rui <wangrui@loongson.cn>
Reviewed-by: Bibo Mao <maobibo@loongson.cn>
Message-Id: <20250418082103.447780-3-wangrui@loongson.cn>
Signed-off-by: Song Gao <gaosong@loongson.cn>