bsd-user/arm/target_arch_cpu.h: Use force_sig_fault for EXCP_UDEF

bsd-user/arm/target_arch_cpu.h: Use force_sig_fault for EXCP_UDEF

Use force_sig_fault to implement unknown opcode. This just uninlines
that function, so simplify things by using it. Fold in EXCP_NOCP and
EXCP_INVSTATE, as is done in linux-user. Make a note about slight
differences with FreeBSD in case any of them turn out to be important
later.

Signed-off-by: Warner Losh <imp@bsdimp.com>
Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>