mxs: Only build internal Ethernet controller for i.MX28

The internal Ethernet controller is only available on i.MX28
processors so it needs to use CONFIG_MX28 guardian to avoid having
this code called in others.

Signed-off-by: Otavio Salvador <otavio@ossystems.com.br>
Acked-by: Marek Vasut <marex@denx.de>

arch/arm/cpu/arm926ejs/mxs/mxs.c

@@ -246,7 +246,7 @@ int do_mx28_showclocks(cmd_tbl_t *cmdtp, int flag, int argc, char *const argv[])
 /*
  * Initializes on-chip ethernet controllers.
  */
-#ifdef	CONFIG_CMD_NET
+#if defined(CONFIG_MX28) && defined(CONFIG_CMD_NET)
 int cpu_eth_init(bd_t *bis)
 {
 	struct mxs_clkctrl_regs *clkctrl_regs =