irqchip/wpcm450: Drop COMPILE_TEST

This driver is (for now) ARM specific, and currently doesn't
build with a variety of architectures (ia64, RISC-V, x86_64
at the very least).

Drop COMPILE_TEST from Kconfig until it gets sorted out.

Reviewed-by: Jonathan Neuschäfer <j.neuschaefer@gmx.net>
Reported-by: Stephen Rothwell <sfr@canb.auug.org.au>
Signed-off-by: Marc Zyngier <maz@kernel.org>