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/sama7g5ek_mmc_defconfig b/configs/sama7g5ek_mmc_defconfig
index e03a6ba..3b62dd3 100644
--- a/configs/sama7g5ek_mmc_defconfig
+++ b/configs/sama7g5ek_mmc_defconfig
@@ -23,6 +23,7 @@
 CONFIG_BOOTCOMMAND="fatload mmc 0:1 0x61000000 at91-sama7g5ek.dtb; fatload mmc 0:1 0x62000000 zImage; bootz 0x62000000 - 0x61000000"
 CONFIG_MISC_INIT_R=y
 CONFIG_HUSH_PARSER=y
+CONFIG_SYS_PBSIZE=276
 CONFIG_CMD_BOOTZ=y
 # CONFIG_CMD_IMI is not set
 CONFIG_CMD_MD5SUM=y