armv7m: use generic arm::core_mode

To simplify things change over to using the generic core_mode struct rather
than maintaining a armv7m specific one.

Change-Id: Ibf32b785d896fef4f33307fabe0d8eb266f7086f
Signed-off-by: Spencer Oliver <spen@spen-soft.co.uk>
Reviewed-on: http://openocd.zylin.com/966
Tested-by: jenkins
Reviewed-by: Andreas Fritiofson <andreas.fritiofson@gmail.com>
armv7m: remove unused armv7m_regtype

This simplifies the armv7m_core_reg structure ready for the move to using
the generic struct arm_reg.

Change-Id: I8edb9d77cc54965d49cd2e754568ebcea4cf6964
Signed-off-by: Spencer Oliver <spen@spen-soft.co.uk>
Reviewed-on: http://openocd.zylin.com/967
Tested-by: jenkins
Reviewed-by: Andreas Fritiofson <andreas.fritiofson@gmail.com>