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/icnova-a20-swac_defconfig b/configs/icnova-a20-swac_defconfig
index de766b2..44080b9 100644
--- a/configs/icnova-a20-swac_defconfig
+++ b/configs/icnova-a20-swac_defconfig
@@ -20,6 +20,7 @@
 CONFIG_VIDEO_LCD_PANEL_LVDS=y
 # CONFIG_SYS_MALLOC_CLEAR_ON_INIT is not set
 CONFIG_SPL_I2C=y
+CONFIG_SYS_PBSIZE=1024
 CONFIG_CMD_UNZIP=y
 CONFIG_SYS_I2C_MVTWSI=y
 CONFIG_SYS_I2C_SLAVE=0x7f