New gdb.reverse test case for aarch64 instructions

New gdb.reverse test case for aarch64 instructions

This patch adds a test case to test the process record for some of
aarch64 instructions.

In each function, GDB turns on process record, and single step until
program goes to the end of the function.  Then, single step backward.
In each of forward single step and backward single step, the contents
of registers are saved, and test compares them.  If there is any
differences, a FAIL is emitted.

The test is flexible, and we can test other instructions easily in the
future.

gdb/testsuite:

2015-05-26  Omair Javaid  <omair.javaid@linaro.org>
	    Yao Qi  <yao.qi@linaro.org>

	* gdb.reverse/aarch64.c: New.
	* gdb.reverse/aarch64.exp: New.