MIPS: Kconfig cleanup

arch/mips/Kconfig already sets GENERIC_HARDIRQS_NO__DO_IRQ unconditionally.
Remove the redundant select from the Loongson Kconfig.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>