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/s5p4418_nanopi2_defconfig b/configs/s5p4418_nanopi2_defconfig
index 4d571ac..cebca74 100644
--- a/configs/s5p4418_nanopi2_defconfig
+++ b/configs/s5p4418_nanopi2_defconfig
@@ -27,6 +27,7 @@
 CONFIG_BOARD_LATE_INIT=y
 CONFIG_HUSH_PARSER=y
 CONFIG_SYS_PROMPT="nanopi2# "
+CONFIG_SYS_PBSIZE=1050
 CONFIG_CMD_BOOTZ=y
 # CONFIG_BOOTM_NETBSD is not set
 # CONFIG_BOOTM_RTEMS is not set