Convert CONFIG_BOOTCOUNT_ENV to Kconfig

This converts the following to Kconfig:
  CONFIG_BOOTCOUNT_ENV

Signed-off-by: Alex Kiernan <alex.kiernan@gmail.com>
Reviewed-by: Lukasz Majewski <lukma@denx.de>
diff --git a/configs/pxm2_defconfig b/configs/pxm2_defconfig
index e689d0f..98edb88 100644
--- a/configs/pxm2_defconfig
+++ b/configs/pxm2_defconfig
@@ -59,6 +59,7 @@
 CONFIG_BOOTP_GATEWAY=y
 CONFIG_BOOTP_SUBNETMASK=y
 CONFIG_BOOTCOUNT_LIMIT=y
+CONFIG_BOOTCOUNT_ENV=y
 CONFIG_DFU_NAND=y
 CONFIG_MMC_OMAP_HS=y
 CONFIG_NAND=y