aarch64: implement rt_sigreturn decoding

* linux/64/syscallent.h (139): Use sys_sigreturn for rt_sigreturn
decoding.
* syscall.c [ARM] (arm_regs): Make static.
[ARM] (arm_sp_ptr): New variable.
[AARCH64] (aarch64_sp_ptr, arm_sp_ptr): New variables.
* linux/aarch64/arch_regs.h: New file.
* linux/arm/arch_regs.h (arm_regs): Remove.
(arm_sp_ptr): New declaration.
* signal.c (sys_sigreturn) [ARM]: Use arm_sp_ptr.
[AARCH64]: Print signal mask.
5 files changed