target/arm: Don't trap WFI/WFE for M profile

target/arm: Don't trap WFI/WFE for M profile

M profile cores can never trap on WFI or WFE instructions. Check for
M profile in check_wfx_trap() to ensure this.

The existing code will do the right thing for v7M cores because
the hcr_el2 and scr_el3 registers will be all-zeroes and so we
won't attempt to trap, but when we start setting ARM_FEATURE_V8
for v8M cores the v8A handling of SCTLR.nTWE and .nTWI will not
give the right results.

Signed-off-by: Peter Maydell <[email protected]>
Reviewed-by: Edgar E. Iglesias <[email protected]>
Reviewed-by: Richard Henderson <[email protected]>
Message-id: 1501692241[email protected]