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/eb_cpu5282_defconfig b/configs/eb_cpu5282_defconfig
index dc649f2..a0cfb1e 100644
--- a/configs/eb_cpu5282_defconfig
+++ b/configs/eb_cpu5282_defconfig
@@ -18,6 +18,7 @@
 CONFIG_MISC_INIT_R=y
 # CONFIG_AUTO_COMPLETE is not set
 CONFIG_SYS_PROMPT="\nEB+CPU5282> "
+CONFIG_SYS_PBSIZE=1054
 CONFIG_CMD_IMLS=y
 CONFIG_CMD_I2C=y
 # CONFIG_CMD_LOADB is not set