target-mips: add microMIPS exception handler support Unlike MIPS16, microMIPS lets you choose the ISA mode for your exception handlers. The ISA mode is selectable via a user-writable CP0.Config3 flag. Signed-off-by: Nathan Froyd <froydnj@codesourcery.com> Signed-off-by: Aurelien Jarno <aurelien@aurel32.net>