MIPS: Rework GENERIC_HARDIRQS Kconfig.

Recent changes to CONFIG_GENERIC_HARDIRQS have caused us to start getting:

warning: (SMP && SYS_SUPPORTS_SMP) selects IRQ_PER_CPU which has unmet direct dependencies (HAVE_GENERIC_HARDIRQS)

Rearranging our Kconfig quiets the message.

Signed-off-by: David Daney <ddaney@caviumnetworks.com>
To: linux-mips@linux-mips.org
Cc: Thomas Gleixner <tglx@linutronix.de>
Patchwork: https://patchwork.linux-mips.org/patch/1757/
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>