xtensa: initialize CPENABLE SR when core has one

XCHAL_CP_NUM is defined in variant/tie.h and it is not included by
head.S, leaving CPENABLE register uninitialised. XCHAL_HAVE_CP is
defined in variant/core.h to 1 when core has CPENABLE SR.

Signed-off-by: Max Filippov <jcmvbkbc@gmail.com>
Signed-off-by: Chris Zankel <chris@zankel.net>
diff --git a/arch/xtensa/kernel/head.S b/arch/xtensa/kernel/head.S
index 0cd337a..91d9095 100644
--- a/arch/xtensa/kernel/head.S
+++ b/arch/xtensa/kernel/head.S
@@ -124,7 +124,7 @@
 
 	/* Disable coprocessors. */
 
-#if XCHAL_CP_NUM > 0
+#if XCHAL_HAVE_CP
 	wsr	a0, cpenable
 #endif