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/trats2_defconfig b/configs/trats2_defconfig
index 6c43a02..a000d80 100644
--- a/configs/trats2_defconfig
+++ b/configs/trats2_defconfig
@@ -24,6 +24,7 @@
 CONFIG_SYS_CONSOLE_INFO_QUIET=y
 CONFIG_MISC_INIT_R=y
 CONFIG_SYS_PROMPT="Trats2 # "
+CONFIG_SYS_PBSIZE=1024
 # CONFIG_CMD_XIMG is not set
 CONFIG_CMD_THOR_DOWNLOAD=y
 CONFIG_CMD_DFU=y