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/tbs2910_defconfig b/configs/tbs2910_defconfig
index 2d9fbd3..1519f7d 100644
--- a/configs/tbs2910_defconfig
+++ b/configs/tbs2910_defconfig
@@ -29,6 +29,7 @@
 CONFIG_HUSH_PARSER=y
 CONFIG_SYS_PROMPT="Matrix U-Boot> "
 CONFIG_SYS_MAXARGS=32
+CONFIG_SYS_PBSIZE=544
 # CONFIG_CMD_BDI is not set
 CONFIG_CMD_BOOTZ=y
 # CONFIG_BOOTM_PLAN9 is not set