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/topic_miamilite_defconfig b/configs/topic_miamilite_defconfig
index fb862b0..5acf1de 100644
--- a/configs/topic_miamilite_defconfig
+++ b/configs/topic_miamilite_defconfig
@@ -30,6 +30,7 @@
 CONFIG_SYS_SPI_U_BOOT_OFFS=0x20000
 CONFIG_SYS_PROMPT="zynq-uboot> "
 CONFIG_SYS_MAXARGS=32
+CONFIG_SYS_PBSIZE=2077
 CONFIG_CMD_THOR_DOWNLOAD=y
 CONFIG_CMD_MEMTEST=y
 CONFIG_CMD_DFU=y