Convert CONFIG_SYS_NAND_PAGE_2K et al to Kconfig

This converts the following to Kconfig:
   CONFIG_SYS_NAND_PAGE_2K
   CONFIG_SYS_NAND_PAGE_4K

Signed-off-by: Tom Rini <trini@konsulko.com>
Reviewed-by: Simon Glass <sjg@chromium.org>
diff --git a/drivers/mtd/nand/raw/Kconfig b/drivers/mtd/nand/raw/Kconfig
index 3585031..5483efe 100644
--- a/drivers/mtd/nand/raw/Kconfig
+++ b/drivers/mtd/nand/raw/Kconfig
@@ -168,6 +168,19 @@
 
 endchoice
 
+choice
+	prompt "NAND page size"
+	depends on NAND_DAVINCI
+	default SYS_NAND_PAGE_2K
+
+config SYS_NAND_PAGE_2K
+	bool "Page size is 2K"
+
+config SYS_NAND_PAGE_4K
+	bool "Page size is 4K"
+
+endchoice
+
 config KEYSTONE_RBL_NAND
 	depends on ARCH_KEYSTONE
 	def_bool y