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/mx7dsabresd_qspi_defconfig b/configs/mx7dsabresd_qspi_defconfig
index 4c4d8a1..c52f45a 100644
--- a/configs/mx7dsabresd_qspi_defconfig
+++ b/configs/mx7dsabresd_qspi_defconfig
@@ -16,6 +16,7 @@
 CONFIG_BOOTCOMMAND="run finduuid; run distro_bootcmd"
 CONFIG_SYS_CONSOLE_IS_IN_ENV=y
 CONFIG_SYS_MAXARGS=32
+CONFIG_SYS_PBSIZE=532
 # CONFIG_CMD_BOOTD is not set
 # CONFIG_BOOTM_NETBSD is not set
 # CONFIG_BOOTM_PLAN9 is not set