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/chromebook_coral_defconfig b/configs/chromebook_coral_defconfig
index 8269254..1111651 100644
--- a/configs/chromebook_coral_defconfig
+++ b/configs/chromebook_coral_defconfig
@@ -51,6 +51,7 @@
 # CONFIG_SPL_SPI_FLASH_TINY is not set
 CONFIG_TPL_POWER=y
 CONFIG_HUSH_PARSER=y
+CONFIG_SYS_PBSIZE=532
 CONFIG_CMD_CPU=y
 CONFIG_CMD_PMC=y
 CONFIG_CMD_GPIO=y