cpus: denver: remove barrier from denver_enable_dco()

This patch removes unnecessary `isb` from the enable DCO sequence as
there is no need to synchronize this operation.

Change-Id: I0191e684bbc7fdba635c3afbc4e4ecd793b6f06f
Signed-off-by: Varun Wadekar <vwadekar@nvidia.com>

lib/cpus/aarch64/denver.S

@@ -59,7 +59,6 @@ func denver_enable_dco
 	mov	x1, #1
 	lsl	x1, x1, x0
 	msr	s3_0_c15_c0_2, x1
-	isb
 	ret
 endfunc denver_enable_dco