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/configs/k2l_evm_defconfig b/configs/k2l_evm_defconfig
index bb91aa3..13d612a 100644
--- a/configs/k2l_evm_defconfig
+++ b/configs/k2l_evm_defconfig
@@ -80,6 +80,7 @@
 CONFIG_SYS_NAND_USE_FLASH_BBT=y
 CONFIG_SYS_NAND_NO_SUBPAGE_WRITE=y
 CONFIG_NAND_DAVINCI=y
+CONFIG_SYS_NAND_PAGE_4K=y
 CONFIG_DM_SPI_FLASH=y
 CONFIG_SF_DEFAULT_SPEED=30000000
 CONFIG_SPI_FLASH_STMICRO=y