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/amcore_defconfig b/configs/amcore_defconfig
index 00620d4..53bfbcf 100644
--- a/configs/amcore_defconfig
+++ b/configs/amcore_defconfig
@@ -18,6 +18,7 @@
 # CONFIG_CMDLINE_EDITING is not set
 # CONFIG_SYS_LONGHELP is not set
 CONFIG_SYS_PROMPT="amcore $ "
+CONFIG_SYS_PBSIZE=282
 # CONFIG_CMD_BOOTD is not set
 CONFIG_CMD_IMLS=y
 # CONFIG_CMD_XIMG is not set