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/apalis-imx8_defconfig b/configs/apalis-imx8_defconfig
index e32e2dd..9f47695 100644
--- a/configs/apalis-imx8_defconfig
+++ b/configs/apalis-imx8_defconfig
@@ -22,6 +22,7 @@
 CONFIG_DISPLAY_BOARDINFO_LATE=y
 CONFIG_BOARD_EARLY_INIT_F=y
 CONFIG_SYS_MAXARGS=64
+CONFIG_SYS_PBSIZE=2068
 CONFIG_CMD_CPU=y
 # CONFIG_BOOTM_NETBSD is not set
 CONFIG_CMD_ASKENV=y