ARM: riscpc: drop support for IOMD_IRQREQC/IOMD_IRQREQD IRQ groups

IOMD_IRQREQC nor IOMD_IRQREQD are ever defined, so any conditionally
compiled code that depends on them is dead code, and can be removed.

Suggested-by: Russell King <linux@armlinux.org.uk>
Signed-off-by: Ard Biesheuvel <ardb@kernel.org>