ARM: mx31: use generic function for displaying silicon revision

Update to use generic function for displaying silicon revision

Tested on mx31pdk board as print the following information:
CPU identified as i.MX31, silicon rev 2.0

Signed-off-by: Jason Liu <jason.hui@linaro.org>
Cc: Fabio Estevam <fabio.estevam@freescale.com>
Cc: Sascha Hauer <s.hauer@pengutronix.de>
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>
diff --git a/arch/arm/mach-imx/clock-imx31.c b/arch/arm/mach-imx/clock-imx31.c
index d973770..85b8885 100644
--- a/arch/arm/mach-imx/clock-imx31.c
+++ b/arch/arm/mach-imx/clock-imx31.c
@@ -611,11 +611,11 @@
 	clk_enable(&gpt_clk);
 	clk_enable(&emi_clk);
 	clk_enable(&iim_clk);
+	mx31_revision();
+	clk_disable(&iim_clk);
 
 	clk_enable(&serial_pll_clk);
 
-	mx31_read_cpu_rev();
-
 	if (mx31_revision() >= IMX_CHIP_REVISION_2_0) {
 		reg = __raw_readl(MXC_CCM_PMCR1);
 		/* No PLL restart on DVFS switch; enable auto EMI handshake */