target/cortex_m: remove wrong xPSR.ICI/IT bits handling

target/cortex_m: remove wrong xPSR.ICI/IT bits handling

If a Cortex-M (not M0, M0+) target was stopped in the middle of
a conditional IT block or in the load/store multiple instruction,
cortex_m_debug_entry() used wrong xPSR bits to detect it and then
cleared 8 bits of the exception number from xPSR
- probably wrong bit mask again.

I believe clearing of the ICI/IT bits in cortex_m_debug_entry() has no
reason as Cortex-M does not use instruction injecting.

Remove the wrong code.

The change was originally a part of http://openocd.zylin.com/4862
It is now re-submitted as #4862 is not ready.

Change-Id: If91cd91d1b81b2684f7d5f10cf20452cde1a7f56
Signed-off-by: Tomas Vanek <vanekt@fbl.cz>
Reviewed-on: http://openocd.zylin.com/5874
Tested-by: jenkins
Reviewed-by: Christopher Head <chead@zaber.com>
Reviewed-by: Antonio Borneo <borneo.antonio@gmail.com>