imx: print ARM clock for clocks command

Default print ARM clock for clocks command.
Test on i.MX6UL 14x14 evk board:
"
=> clocks
PLL_SYS         792 MHz
PLL_BUS         528 MHz
PLL_OTG         480 MHz
PLL_NET          50 MHz

ARM          396000 kHz
"

Signed-off-by: Peng Fan <van.freenix@gmail.com>
Cc: Stefano Babic <sbabic@denx.de>

arch/arm/cpu/armv7/mx6/clock.c

@@ -1183,6 +1183,7 @@ int do_mx6_showclocks(cmd_tbl_t *cmdtp, int flag, int argc, char * const argv[])
 	printf("PLL_NET    %8d MHz\n", freq / 1000000);
 
 	printf("\n");
+	printf("ARM        %8d kHz\n", mxc_get_clock(MXC_ARM_CLK) / 1000);
 	printf("IPG        %8d kHz\n", mxc_get_clock(MXC_IPG_CLK) / 1000);
 	printf("UART       %8d kHz\n", mxc_get_clock(MXC_UART_CLK) / 1000);
 #ifdef CONFIG_MXC_SPI