Blackfin: small cpu init optimization while setting interrupt mask

Use the sti instruction to set the initial interrupt mask rather than
banging on the core IMASK MMR to save both space and time.

Signed-off-by: Mike Frysinger <vapier@gentoo.org>

cpu/blackfin/start.S

@@ -193,11 +193,8 @@ ENTRY(_start)
 	p1.l = .Lenable_nested;
 	p1.h = .Lenable_nested;
 	[p0] = p1;
-	p2.l = LO(IMASK);
-	p2.h = HI(IMASK);
-	p3.l = LO(EVT_IVG15);
-	p3.h = HI(EVT_IVG15);
-	[p2] = p3;
+	r7 = EVT_IVG15 (z);
+	sti r7;
 	raise 15;
 	p4.l = .LWAIT_HERE;
 	p4.h = .LWAIT_HERE;