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/lx2160ardb_tfa_stmm_defconfig b/configs/lx2160ardb_tfa_stmm_defconfig
index b1d8438..5589c48 100644
--- a/configs/lx2160ardb_tfa_stmm_defconfig
+++ b/configs/lx2160ardb_tfa_stmm_defconfig
@@ -38,6 +38,7 @@
 CONFIG_MISC_INIT_R=y
 CONFIG_RESET_PHY_R=y
 CONFIG_SYS_MAXARGS=64
+CONFIG_SYS_PBSIZE=532
 CONFIG_CMD_GREPENV=y
 CONFIG_CMD_NVEDIT_EFI=y
 CONFIG_CMD_EEPROM=y