riscv: Make regs_irqs_disabled() more clear

riscv: Make regs_irqs_disabled() more clear

The return value of regs_irqs_disabled() is true or false, so change
its type to reflect that and also make it always inline.

Suggested-by: Huacai Chen <chenhuacai@loongson.cn>
Signed-off-by: Tiezhu Yang <yangtiezhu@loongson.cn>
Reviewed-by: Alexandre Ghiti <alexghiti@rivosinc.com>
Link: https://lore.kernel.org/r/20250422113156.25742-1-yangtiezhu@loongson.cn
Signed-off-by: Alexandre Ghiti <alexghiti@rivosinc.com>
Signed-off-by: Palmer Dabbelt <palmer@dabbelt.com>