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/pogo_e02_defconfig b/configs/pogo_e02_defconfig
index d512fd4..699e8e2 100644
--- a/configs/pogo_e02_defconfig
+++ b/configs/pogo_e02_defconfig
@@ -21,6 +21,7 @@
 # CONFIG_DISPLAY_BOARDINFO is not set
 CONFIG_SYS_PROMPT="PogoE02> "
 CONFIG_SYS_MAXARGS=32
+CONFIG_SYS_PBSIZE=1050
 # CONFIG_CMD_FLASH is not set
 CONFIG_CMD_NAND=y
 CONFIG_CMD_USB=y