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/sama5d3xek_nandflash_defconfig b/configs/sama5d3xek_nandflash_defconfig
index b8557aa..62edd2d 100644
--- a/configs/sama5d3xek_nandflash_defconfig
+++ b/configs/sama5d3xek_nandflash_defconfig
@@ -72,6 +72,7 @@
 CONFIG_PMECC_CAP=4
 CONFIG_SPL_GENERATE_ATMEL_PMECC_HEADER=y
 CONFIG_SYS_NAND_BLOCK_SIZE=0x20000
+CONFIG_SYS_NAND_PAGE_COUNT=0x40
 CONFIG_SYS_NAND_PAGE_SIZE=0x800
 CONFIG_SYS_NAND_OOBSIZE=0x40
 CONFIG_DM_SPI_FLASH=y