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/bubblegum_96_defconfig b/configs/bubblegum_96_defconfig
index 33402f2..f577ec0 100644
--- a/configs/bubblegum_96_defconfig
+++ b/configs/bubblegum_96_defconfig
@@ -15,6 +15,7 @@
 # CONFIG_DISPLAY_BOARDINFO is not set
 CONFIG_SYS_PROMPT="U-Boot => "
 CONFIG_SYS_MAXARGS=64
+CONFIG_SYS_PBSIZE=1051
 CONFIG_CMD_MD5SUM=y
 CONFIG_CMD_MEMINFO=y
 CONFIG_CMD_CACHE=y