Hi,

This patch moves the existing sysreg tests for AArch64 into a subdirectory
(sysreg). The number of test files related to system registers grew
relatively big with time and makes the browsing of those files difficult.
Moreover, the difference of naming for the failure, working, and
feature-specific scenarios causes the tests not to appear next to one
another in the exploration tree when it is ordered alphabetically.

Regression tested on the aarch64-none-elf, and and no regressions was found.

Ok for binutils-master? I don't have commit access so I need someone to 
commit on my behalf.

Regards,
Matthieu.