Convert CONFIG_SYS_PBSIZE to Kconfig

This converts the following to Kconfig:
   CONFIG_SYS_PBSIZE

Signed-off-by: Tom Rini <trini@konsulko.com>
diff --git a/configs/nas220_defconfig b/configs/nas220_defconfig
index a3129fb..ba82b08 100644
--- a/configs/nas220_defconfig
+++ b/configs/nas220_defconfig
@@ -21,6 +21,7 @@
 CONFIG_HUSH_PARSER=y
 CONFIG_SYS_PROMPT="nas220> "
 CONFIG_SYS_MAXARGS=32
+CONFIG_SYS_PBSIZE=1049
 # CONFIG_CMD_FLASH is not set
 CONFIG_CMD_IDE=y
 CONFIG_CMD_NAND=y