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/rock_defconfig b/configs/rock_defconfig
index 5c29548..37cd5c5 100644
--- a/configs/rock_defconfig
+++ b/configs/rock_defconfig
@@ -12,6 +12,7 @@
 CONFIG_DEBUG_UART_BASE=0x20064000
 CONFIG_DEBUG_UART_CLOCK=24000000
 CONFIG_DEBUG_UART=y
+CONFIG_USE_PREBOOT=y
 CONFIG_DEFAULT_FDT_FILE="rk3188-radxarock.dtb"
 # CONFIG_DISPLAY_CPUINFO is not set
 CONFIG_DISPLAY_BOARDINFO_LATE=y