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/kp_imx6q_tpc_defconfig b/configs/kp_imx6q_tpc_defconfig
index bdc3954..012a5c4 100644
--- a/configs/kp_imx6q_tpc_defconfig
+++ b/configs/kp_imx6q_tpc_defconfig
@@ -30,6 +30,7 @@
 CONFIG_SPL_POWER=y
 CONFIG_SPL_WATCHDOG=y
 CONFIG_SYS_MAXARGS=32
+CONFIG_SYS_PBSIZE=532
 # CONFIG_CMD_ELF is not set
 CONFIG_CMD_GPIO=y
 CONFIG_CMD_I2C=y