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/nanopi_a64_defconfig b/configs/nanopi_a64_defconfig
index eb031e6..95a9c96 100644
--- a/configs/nanopi_a64_defconfig
+++ b/configs/nanopi_a64_defconfig
@@ -5,6 +5,7 @@
 CONFIG_MACH_SUN50I=y
 CONFIG_RESERVE_ALLWINNER_BOOT0_HEADER=y
 # CONFIG_SYS_MALLOC_CLEAR_ON_INIT is not set
+CONFIG_USE_PREBOOT=y
 # CONFIG_CMD_FLASH is not set
 # CONFIG_SPL_DOS_PARTITION is not set
 # CONFIG_SPL_EFI_PARTITION is not set