target-arm: Separate out M profile cpu_exec_interrupt handling

target-arm: Separate out M profile cpu_exec_interrupt handling

The M profile cpu_exec_interrupt handling is fairly simple
but does include an M profile specific oddity (disabling
interrupts for certain PC values). A/R profile handling
on the other hand is getting rapidly more complicated
with the support for EL2 and EL3. Split the M profile
code out into its own implementation of cpu_exec_interrupt
to keep these two things out of each others' way.

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Edgar E. Iglesias <edgar.iglesias@xilinx.com>
Message-id: 1414684132-23971-2-git-send-email-peter.maydell@linaro.org