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/mk802_defconfig b/configs/mk802_defconfig
index 416565e..281130a 100644
--- a/configs/mk802_defconfig
+++ b/configs/mk802_defconfig
@@ -5,6 +5,7 @@
 CONFIG_MACH_SUN4I=y
 CONFIG_USB2_VBUS_PIN="PH12"
 # CONFIG_SYS_MALLOC_CLEAR_ON_INIT is not set
+CONFIG_SYS_PBSIZE=1024
 CONFIG_SYS_I2C_MVTWSI=y
 CONFIG_SYS_I2C_SLAVE=0x7f
 CONFIG_SYS_I2C_SPEED=400000