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/rpi_defconfig b/configs/rpi_defconfig
index 0fe4ec4..014898a 100644
--- a/configs/rpi_defconfig
+++ b/configs/rpi_defconfig
@@ -16,6 +16,7 @@
 CONFIG_MISC_INIT_R=y
 CONFIG_FDT_SIMPLEFB=y
 CONFIG_SYS_PROMPT="U-Boot> "
+CONFIG_SYS_PBSIZE=1049
 CONFIG_CMD_GPIO=y
 CONFIG_CMD_MMC=y
 CONFIG_CMD_USB=y