Convert CONFIG_BOARD_SIZE_LIMIT to Kconfig

This converts the following to Kconfig:
   CONFIG_BOARD_SIZE_LIMIT

To do this, introduce CONFIG_HAS_BOARD_SIZE_LIMIT.

Signed-off-by: Tom Rini <trini@konsulko.com>
diff --git a/configs/pico-dwarf-imx6ul_defconfig b/configs/pico-dwarf-imx6ul_defconfig
index 3a03081..8e1c25d 100644
--- a/configs/pico-dwarf-imx6ul_defconfig
+++ b/configs/pico-dwarf-imx6ul_defconfig
@@ -19,6 +19,8 @@
 CONFIG_SYS_MEMTEST_START=0x80000000
 CONFIG_SYS_MEMTEST_END=0x88000000
 CONFIG_DISTRO_DEFAULTS=y
+CONFIG_HAS_BOARD_SIZE_LIMIT=y
+CONFIG_BOARD_SIZE_LIMIT=715776
 CONFIG_BOOTDELAY=3
 CONFIG_BOOTCOMMAND="run findfdt; run finduuid; run distro_bootcmd"
 CONFIG_DEFAULT_FDT_FILE="imx6ul-pico-dwarf.dtb"