ARM11: use shared DSCR bit names

ARM11: use shared DSCR bit names

For the bits now defined in "arm_dpm.h", switch to the
shared DSCR_* symbol and remove the ARM11_DSCR_* version.

Define DSCR_INT_DIS and use it instead of the ARM11_DSCR_*
sibling symbol.  (Note:  for both ARM11 and Cortex-A8, this
should arguably be enabled by default when single stepping.)

Remove some other unused declarations in "arm11.h".

Signed-off-by: David Brownell <dbrownell@users.sourceforge.net>