arm: Remove zmx25 board and ARCH_MX25

This board has not been converted to CONFIG_DM by the deadline.
Remove it.  As this is the last ARCH_MX25 platform, remove those
references as well.

Cc: Matthias Weisser <weisserm@arcor.de>
Cc: Stefano Babic <sbabic@denx.de>
Signed-off-by: Tom Rini <trini@konsulko.com>
diff --git a/drivers/serial/Kconfig b/drivers/serial/Kconfig
index cbea165..3bb5b02 100644
--- a/drivers/serial/Kconfig
+++ b/drivers/serial/Kconfig
@@ -645,7 +645,7 @@
 
 config MXC_UART
 	bool "IMX serial port support"
-	depends on ARCH_MX25 || ARCH_MX31 || MX5 || MX6 || MX7 || IMX8M
+	depends on ARCH_MX31 || MX5 || MX6 || MX7 || IMX8M
 	help
 	  If you have a machine based on a Motorola IMX CPU you
 	  can enable its onboard serial port by enabling this option.