Make hypercalls arch-independent.

Clean up the hypercall code to make the code in hypercalls.c
architecture independent. First process the common hypercalls and
then call lguest_arch_do_hcall() if the call hasn't been handled.
Rename struct hcall_ring to hcall_args.

This patch requires the previous patch which reorganize the layout of
struct lguest_regs on i386 so they match the layout of struct
hcall_args.

Signed-off-by: Jes Sorensen <jes@sgi.com>
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
diff --git a/include/linux/lguest.h b/include/linux/lguest.h
index 8e959de..ea335c8 100644
--- a/include/linux/lguest.h
+++ b/include/linux/lguest.h
@@ -36,7 +36,7 @@
 	/* 0xFF == done (set by Host), 0 == pending (set by Guest). */
 	u8 hcall_status[LHCALL_RING_SIZE];
 	/* The actual registers for the hypercalls. */
-	struct hcall_ring hcalls[LHCALL_RING_SIZE];
+	struct hcall_args hcalls[LHCALL_RING_SIZE];
 
 /* Fields initialized by the Host at boot: */
 	/* Memory not to try to access */