gdb/testsuite/gdb.base: Enable disp-step-syscall.exp tests for ARM.

gdb/testsuite/gdb.base: Enable disp-step-syscall.exp tests for ARM.

disp-step-syscall.exp is not run for ARM targets because ARM syscall
instructions have not been added to the list of possible syscall
instructions. This patch adds ARM syscall instructions to enable
disp-step-syscall.exp tests for ARM targets. Attached patch is tested
on ARMv7 and helps pass all disp-step-syscall.exp tests for ARM
targets.

gdb/testsuite/ChangeLog:

2013-07-19  Omair Javaid  <Omair.Javaid@linaro.org>

	* gdb.base/disp-step-syscall.exp: Add svc and swi syscall
	instructions and enable disp-step-syscall for arm targets.