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/colibri_imx7_emmc_defconfig b/configs/colibri_imx7_emmc_defconfig
index cef48b9..361077e 100644
--- a/configs/colibri_imx7_emmc_defconfig
+++ b/configs/colibri_imx7_emmc_defconfig
@@ -25,6 +25,7 @@
 CONFIG_BOARD_LATE_INIT=y
 CONFIG_SYS_PROMPT="Colibri iMX7 # "
 CONFIG_SYS_MAXARGS=32
+CONFIG_SYS_PBSIZE=544
 # CONFIG_CMD_BOOTD is not set
 # CONFIG_BOOTM_PLAN9 is not set
 # CONFIG_BOOTM_RTEMS is not set