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/stih410-b2260_defconfig b/configs/stih410-b2260_defconfig
index 642c199..a0b1e0d 100644
--- a/configs/stih410-b2260_defconfig
+++ b/configs/stih410-b2260_defconfig
@@ -16,6 +16,7 @@
 CONFIG_BOOTARGS="console=ttyAS1,115200 CONSOLE=/dev/ttyAS1 consoleblank=0 root=/dev/mmcblk0p2 rootfstype=ext4 rw rootwait mem=992M@0x40000000 vmalloc=256m"
 # CONFIG_DISPLAY_CPUINFO is not set
 CONFIG_SYS_PROMPT="stih410-b2260 => "
+CONFIG_SYS_PBSIZE=1058
 CONFIG_CMD_ASKENV=y
 CONFIG_CMD_GPT=y
 CONFIG_CMD_MMC=y