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/lx2160aqds_tfa_SECURE_BOOT_defconfig b/configs/lx2160aqds_tfa_SECURE_BOOT_defconfig
index 03a3c84..abb095d 100644
--- a/configs/lx2160aqds_tfa_SECURE_BOOT_defconfig
+++ b/configs/lx2160aqds_tfa_SECURE_BOOT_defconfig
@@ -35,6 +35,7 @@
 CONFIG_MISC_INIT_R=y
 CONFIG_RESET_PHY_R=y
 CONFIG_SYS_MAXARGS=64
+CONFIG_SYS_PBSIZE=532
 CONFIG_CMD_GREPENV=y
 CONFIG_CMD_EEPROM=y
 CONFIG_SYS_EEPROM_PAGE_WRITE_BITS=3