Convert CONFIG_SYS_NAND_PAGE_COUNT to Kconfig

This converts the following to Kconfig:
   CONFIG_SYS_NAND_PAGE_COUNT

Signed-off-by: Tom Rini <trini@konsulko.com>
diff --git a/configs/sama5d4_xplained_nandflash_defconfig b/configs/sama5d4_xplained_nandflash_defconfig
index 94a2e8e..7a3d6fb 100644
--- a/configs/sama5d4_xplained_nandflash_defconfig
+++ b/configs/sama5d4_xplained_nandflash_defconfig
@@ -67,6 +67,7 @@
 CONFIG_PMECC_CAP=8
 CONFIG_SPL_GENERATE_ATMEL_PMECC_HEADER=y
 CONFIG_SYS_NAND_BLOCK_SIZE=0x40000
+CONFIG_SYS_NAND_PAGE_COUNT=0x40
 CONFIG_SYS_NAND_PAGE_SIZE=0x1000
 CONFIG_SYS_NAND_OOBSIZE=0xe0
 CONFIG_DM_SPI_FLASH=y