depthcharge: Update build

- Add prompt so the defconfig can be selected for the build.
- Remove target rename code from makefile.  The old versions don't build
with the latest vboot, so this isn't useful anymore.
- Change $(info ...) to an echo.  info prints immediately when
evaluated, which made it print when it shouldn't have, on make clean
for example.
- Split up single line shell scripts into multiple lines
- Change checkout target to only update the commit id when actually
changing versions instead of on every build.

Change-Id: I46fc2822cf93c821b402e8961ceecedc088f486c
Signed-off-by: Martin Roth <martinroth@google.com>
Reviewed-on: https://review.coreboot.org/20667
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Marshall Dawson <marshalldawson3rd@gmail.com>

payloads/external/depthcharge/Kconfig

@@ -36,7 +36,7 @@ config PAYLOAD_FILE
 	default "payloads/external/depthcharge/depthcharge/build/depthcharge.elf"
 
 config LP_DEFCONFIG_OVERRIDE
-	def_bool n
+	bool "Use default libpayload config"
 	help
 	  The Depthcharge makefile looks for a file config.<boardname> in the
 	  libpayload/configs directory.  Say Y here to use the file defconfig