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/T2080QDS_SECURE_BOOT_defconfig b/configs/T2080QDS_SECURE_BOOT_defconfig
index 0464557..d9822ba 100644
--- a/configs/T2080QDS_SECURE_BOOT_defconfig
+++ b/configs/T2080QDS_SECURE_BOOT_defconfig
@@ -25,6 +25,7 @@
 CONFIG_BOOTCOMMAND="setenv bootargs root=/dev/ram rw console=$consoledev,$baudrate $othbootargs;setenv ramdiskaddr 0x02000000;setenv fdtaddr 0x00c00000;setenv loadaddr 0x1000000;bootm $loadaddr $ramdiskaddr $fdtaddr"
 CONFIG_BOARD_EARLY_INIT_R=y
 CONFIG_HUSH_PARSER=y
+CONFIG_SYS_PBSIZE=276
 CONFIG_CMD_IMLS=y
 CONFIG_CMD_GREPENV=y
 CONFIG_CMD_I2C=y