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/cm_t43_defconfig b/configs/cm_t43_defconfig
index 0a64d1d..c3ddc5e 100644
--- a/configs/cm_t43_defconfig
+++ b/configs/cm_t43_defconfig
@@ -41,6 +41,7 @@
 CONFIG_SYS_SPI_U_BOOT_OFFS=0x40000
 CONFIG_SYS_PROMPT="CM-T43 # "
 CONFIG_SYS_MAXARGS=64
+CONFIG_SYS_PBSIZE=1050
 CONFIG_CMD_ASKENV=y
 CONFIG_CMD_EEPROM=y
 CONFIG_CMD_EEPROM_LAYOUT=y