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/colibri_vf_defconfig b/configs/colibri_vf_defconfig
index c5f4322..d92756f 100644
--- a/configs/colibri_vf_defconfig
+++ b/configs/colibri_vf_defconfig
@@ -29,6 +29,7 @@
 CONFIG_HUSH_PARSER=y
 # CONFIG_SYS_LONGHELP is not set
 CONFIG_SYS_PROMPT="Colibri VFxx # "
+CONFIG_SYS_PBSIZE=1056
 # CONFIG_CMD_BOOTD is not set
 # CONFIG_CMD_BOOTM is not set
 CONFIG_CMD_BOOTZ=y