arm64: use {COMPAT,}SYSCALL_DEFINE0 for sigreturn

We don't currently annotate our various sigreturn functions as syscalls,
as we need to do to use pt_regs syscall wrappers.

Let's mark them as real syscalls.

For compat_sys_sigreturn and compat_sys_rt_sigreturn, this changes the
return type from int to long, matching the prototypes in sys32.c.

Signed-off-by: Mark Rutland <mark.rutland@arm.com>
Reviewed-by: Dominik Brodowski <linux@dominikbrodowski.net>
Acked-by: Catalin Marinas <catalin.marinas@arm.com>
Cc: Will Deacon <will.deacon@arm.com>
Signed-off-by: Will Deacon <will.deacon@arm.com>

arch/arm64/kernel/signal.c

@@ -539,7 +539,7 @@ static int restore_sigframe(struct pt_regs *regs,
 	return err;
 }
 
-asmlinkage long sys_rt_sigreturn(void)
+SYSCALL_DEFINE0(rt_sigreturn)
 {
 	struct pt_regs *regs = current_pt_regs();
 	struct rt_sigframe __user *frame;

arch/arm64/kernel/signal32.c

@@ -285,7 +285,7 @@ static int compat_restore_sigframe(struct pt_regs *regs,
 	return err;
 }
 
-asmlinkage int compat_sys_sigreturn(void)
+COMPAT_SYSCALL_DEFINE0(sigreturn)
 {
 	struct pt_regs *regs = current_pt_regs();
 	struct compat_sigframe __user *frame;
@@ -316,7 +316,7 @@ badframe:
 	return 0;
 }
 
-asmlinkage int compat_sys_rt_sigreturn(void)
+COMPAT_SYSCALL_DEFINE0(rt_sigreturn)
 {
 	struct pt_regs *regs = current_pt_regs();
 	struct compat_rt_sigframe __user *frame;