Preserve the registers containing argc, argv, and return address values

passed in from u-boot across the call to self_reloc and any other early-init
code, and restore them before calling main().

The self_reloc() routine uses r0 and r1 (and calling it uses lr), and
depending on what values get left in them, main() would intermittantly lock
up trying to interpret them as argc and argv values.  This problem affected
the self-relocatable ubldr.bin but not ubldr (the elf version).

sys/boot/arm/uboot/start.S

@@ -45,6 +45,13 @@ _start:
 	orr	ip, ip, #(CPU_CONTROL_AFLT_ENABLE)
 	mcr     p15, 0, ip, c1, c0, 0
 #endif
+
+	/*
+	 * Save r0 and r1 (argc and argv passed from u-boot), and lr (trashed
+	 * by the call to self_reloc below) until we're ready to call main().
+	 */
+	push	{r0, r1, lr}
+
 	/* 
 	 * Do self-relocation when the weak external symbol _DYNAMIC is non-NULL.
 	 * When linked as a dynamic relocatable file, the linker automatically
@@ -71,9 +78,11 @@ _start:
 	str	r9, [ip, #4]
 
 	/* 
+	 * First restore argc, argv, and the u-boot return address, then
 	 * Start loader.  This is basically a tail-recursion call; if main()
 	 * returns, it returns to u-boot (which reports the value returned r0).
 	 */
+	pop	{r0, r1, lr}
 	b	main
 
 	/*