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/stm32mp15-icore-stm32mp1-ctouch2_defconfig b/configs/stm32mp15-icore-stm32mp1-ctouch2_defconfig
index 7bf24cf..122fe36 100644
--- a/configs/stm32mp15-icore-stm32mp1-ctouch2_defconfig
+++ b/configs/stm32mp15-icore-stm32mp1-ctouch2_defconfig
@@ -21,6 +21,7 @@
 CONFIG_SPL_I2C=y
 CONFIG_SPL_POWER=y
 CONFIG_SYS_PROMPT="STM32MP> "
+CONFIG_SYS_PBSIZE=1050
 CONFIG_CMD_ADTIMG=y
 CONFIG_CMD_ERASEENV=y
 CONFIG_CMD_MEMINFO=y