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/mccmon6_sd_defconfig b/configs/mccmon6_sd_defconfig
index 5020b87..0f17ccd 100644
--- a/configs/mccmon6_sd_defconfig
+++ b/configs/mccmon6_sd_defconfig
@@ -28,6 +28,7 @@
 CONFIG_SPL_ENV_SUPPORT=y
 CONFIG_SPL_NOR_SUPPORT=y
 CONFIG_SYS_MAXARGS=32
+CONFIG_SYS_PBSIZE=532
 CONFIG_CMD_SPL=y
 CONFIG_CMD_SPL_NOR_OFS=0x09600000
 CONFIG_CMD_SPL_WRITE_SIZE=0x20000