arch/tile: eliminate pt_regs trampolines for syscalls

Using the new current_pt_regs() model, we can remove some trampolines
from assembly code and call directly to the C syscall implementations.
rt_sigreturn() and clone() still need some assembly wrapping, but no
longer are passed a pt_regs pointer.  sigaltstack() and the
tilepro-specific cmpxchg_badaddr() syscalls are now just straight C.

Signed-off-by: Chris Metcalf <cmetcalf@tilera.com>
diff --git a/arch/tile/kernel/process.c b/arch/tile/kernel/process.c
index 58f8fd1..6e7fb4e 100644
--- a/arch/tile/kernel/process.c
+++ b/arch/tile/kernel/process.c
@@ -584,10 +584,10 @@
 }
 
 /* Note there is an implicit fifth argument if (clone_flags & CLONE_SETTLS). */
-SYSCALL_DEFINE5(clone, unsigned long, clone_flags, unsigned long, newsp,
-		void __user *, parent_tidptr, void __user *, child_tidptr,
-		struct pt_regs *, regs)
+SYSCALL_DEFINE4(clone, unsigned long, clone_flags, unsigned long, newsp,
+		void __user *, parent_tidptr, void __user *, child_tidptr)
 {
+	struct pt_regs *regs = current_pt_regs();
 	if (!newsp)
 		newsp = regs->sp;
 	return do_fork(clone_flags, newsp, regs, 0,