Convert CONFIG_USE_PREBOOT and CONFIG_PREBOOT to Kconfig

This converts the following to Kconfig:
   CONFIG_USE_PREBOOT
   CONFIG_PREBOOT

Both are together in one commit, since otherwise the former causes kconfig
to define the latter, which gives duplicate symbol errors.

Includes a manual fixup for CONFIG_PREBOOT in ids8313_defconfig since the
backslash lands in the wrong place. Similarly with socfpga_vining_fpga.

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/configs/gwventana_emmc_defconfig b/configs/gwventana_emmc_defconfig
index 19aa73f..70b663a 100644
--- a/configs/gwventana_emmc_defconfig
+++ b/configs/gwventana_emmc_defconfig
@@ -18,6 +18,7 @@
 CONFIG_OF_BOARD_SETUP=y
 CONFIG_SYS_EXTRA_OPTIONS="IMX_CONFIG=arch/arm/mach-imx/spl_sd.cfg"
 CONFIG_BOOTDELAY=3
+CONFIG_USE_PREBOOT=y
 CONFIG_SUPPORT_RAW_INITRD=y
 CONFIG_MISC_INIT_R=y
 # CONFIG_DISPLAY_BOARDINFO is not set