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/r8a77970_eagle_defconfig b/configs/r8a77970_eagle_defconfig
index b6a113a..4f4bd7a 100644
--- a/configs/r8a77970_eagle_defconfig
+++ b/configs/r8a77970_eagle_defconfig
@@ -23,6 +23,7 @@
 CONFIG_DEFAULT_FDT_FILE="r8a77970-eagle.dtb"
 CONFIG_HUSH_PARSER=y
 CONFIG_SYS_MAXARGS=64
+CONFIG_SYS_PBSIZE=2068
 CONFIG_CMD_BOOTZ=y
 CONFIG_CMD_DFU=y
 CONFIG_CMD_GPIO=y