Convert CONFIG_LPUART et al to Kconfig

This converts the following to Kconfig:
   CONFIG_LPUART
   CONFIG_LPUART_32B_REG

And note that CONFIG_LPUART_32B_REG is unused in code.

Signed-off-by: Tom Rini <trini@konsulko.com>
diff --git a/drivers/serial/Kconfig b/drivers/serial/Kconfig
index 345d188..610f806 100644
--- a/drivers/serial/Kconfig
+++ b/drivers/serial/Kconfig
@@ -647,6 +647,10 @@
 	  Select this to enable a Low Power UART for Freescale VF610 and
 	  QorIQ Layerscape devices.
 
+config LPUART
+	bool "Use the LPUART as console"
+	depends on FSL_LPUART
+
 config MVEBU_A3700_UART
 	bool "UART support for Armada 3700"
 	help