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/a3y17lte_defconfig b/configs/a3y17lte_defconfig
index 536e23e..5a2a46e 100644
--- a/configs/a3y17lte_defconfig
+++ b/configs/a3y17lte_defconfig
@@ -17,6 +17,7 @@
 CONFIG_SAVE_PREV_BL_INITRAMFS_START_ADDR=y
 # CONFIG_DISPLAY_CPUINFO is not set
 CONFIG_HUSH_PARSER=y
+CONFIG_SYS_PBSIZE=1024
 CONFIG_CMD_GPIO=y
 CONFIG_CMD_I2C=y
 CONFIG_DM_I2C_GPIO=y