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/da850evm_defconfig b/configs/da850evm_defconfig
index bfc8488..a692e14 100644
--- a/configs/da850evm_defconfig
+++ b/configs/da850evm_defconfig
@@ -40,6 +40,7 @@
 CONFIG_SYS_SPI_U_BOOT_OFFS=0x8000
 CONFIG_HUSH_PARSER=y
 CONFIG_SYS_PROMPT="U-Boot > "
+CONFIG_SYS_PBSIZE=1050
 CONFIG_CRC32_VERIFY=y
 CONFIG_CMD_MX_CYCLIC=y
 CONFIG_CMD_DM=y