i.MX31: Start the I2C clock on driver initialisation

i.MX31 powers on with most clocks running, so, after a power on this explicit
clock start up is not required. However, as Linux boots it disables most clocks
to save power. This includes the I2C clock. If we then soft reboot from Linux
the I2C clock stays off. This breaks the phycore, which has its environment in
I2C EEPROM. Fix the problem by explicitly starting the clock in I2C driver
initialisation routine.

Signed-off-by: Guennadi Liakhovetski <lg@denx.de>
Ack-by: Jean-Christophe PLAGNIOL-VILLARD <plagnioj@jcrosoft.com>

drivers/i2c/mxc_i2c.c

@@ -49,10 +49,13 @@
 
 #ifdef CONFIG_SYS_I2C_MX31_PORT1
 #define I2C_BASE	0x43f80000
+#define I2C_CLK_OFFSET	26
 #elif defined (CONFIG_SYS_I2C_MX31_PORT2)
 #define I2C_BASE	0x43f98000
+#define I2C_CLK_OFFSET	28
 #elif defined (CONFIG_SYS_I2C_MX31_PORT3)
 #define I2C_BASE	0x43f84000
+#define I2C_CLK_OFFSET	30
 #else
 #error "define CONFIG_SYS_I2C_MX31_PORTx to use the mx31 I2C driver"
 #endif
@@ -72,6 +75,9 @@ void i2c_init(int speed, int unused)
 	int freq = mx31_get_ipg_clk();
 	int i;
 
+	/* start the required I2C clock */
+	__REG(CCM_CGR0) = __REG(CCM_CGR0) | (3 << I2C_CLK_OFFSET);
+
 	for (i = 0; i < 0x1f; i++)
 		if (freq / div[i] <= speed)
 			break;