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/mx6qsabrelite_defconfig b/configs/mx6qsabrelite_defconfig
index 0d402f2..65e9c4f 100644
--- a/configs/mx6qsabrelite_defconfig
+++ b/configs/mx6qsabrelite_defconfig
@@ -8,6 +8,7 @@
 CONFIG_SYS_EXTRA_OPTIONS="IMX_CONFIG=board/boundary/nitrogen6x/nitrogen6q.cfg,MX6Q,DDR_MB=1024,SABRELITE"
 CONFIG_BOOTDELAY=3
 # CONFIG_USE_BOOTCOMMAND is not set
+CONFIG_USE_PREBOOT=y
 CONFIG_SYS_CONSOLE_OVERWRITE_ROUTINE=y
 CONFIG_MISC_INIT_R=y
 CONFIG_BOUNCE_BUFFER=y