ARM: nwfpe: allow debugging output to be configured at runtime

Enabling CONFIG_USER_DEBUG allows NWFPE to complain about every FP
exception, which with some programs can cause the kernel message log
to fill with NWFPE debug, swamping out other messages.

This change allows NWFPE debugging to be configured at run time.

Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>