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/imx8mq_cm_defconfig b/configs/imx8mq_cm_defconfig
index 4155a47..4c8eeca 100644
--- a/configs/imx8mq_cm_defconfig
+++ b/configs/imx8mq_cm_defconfig
@@ -33,6 +33,7 @@
 CONFIG_SPL_I2C=y
 CONFIG_SYS_PROMPT="u-boot=> "
 CONFIG_SYS_MAXARGS=64
+CONFIG_SYS_PBSIZE=1050
 CONFIG_CMD_FUSE=y
 CONFIG_CMD_GPIO=y
 CONFIG_CMD_I2C=y