xregs_sig: Add a ability to handle multiple register banks

[dchagin]

Summary

While here replace the .global directive by traditionally used .globl.

[kib]

tools/test/xregs_sig/c2x2c_aarch64.S

7–8

I think you should also add the .text directive there

tools/test/xregs_sig/c2x2c_amd64.S

7–8

Also .text

tools/test/xregs_sig/xregs_sig.c

61

[dchagin]

Done, .text added

[kib]

tools/test/xregs_sig/xregs_sig.c

61

And what about this?

[dchagin]

whoops, missed it due to phabric email doesn't show it,
constify struct xregs_banks, thank you