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/T1024RDB_SDCARD_defconfig b/configs/T1024RDB_SDCARD_defconfig
index a820d29..9a3e19a 100644
--- a/configs/T1024RDB_SDCARD_defconfig
+++ b/configs/T1024RDB_SDCARD_defconfig
@@ -39,6 +39,7 @@
 CONFIG_SPL_I2C=y
 CONFIG_SPL_MPC8XXX_INIT_DDR=y
 CONFIG_HUSH_PARSER=y
+CONFIG_SYS_PBSIZE=276
 CONFIG_CMD_IMLS=y
 CONFIG_CMD_GREPENV=y
 CONFIG_SYS_I2C_EEPROM_ADDR_LEN=2