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/ib62x0_defconfig b/configs/ib62x0_defconfig
index a2994b3..5e3e26d 100644
--- a/configs/ib62x0_defconfig
+++ b/configs/ib62x0_defconfig
@@ -21,6 +21,7 @@
 CONFIG_HUSH_PARSER=y
 CONFIG_SYS_PROMPT="ib62x0 => "
 CONFIG_SYS_MAXARGS=32
+CONFIG_SYS_PBSIZE=1051
 CONFIG_CMD_BOOTZ=y
 # CONFIG_CMD_FLASH is not set
 CONFIG_CMD_IDE=y