RISCV: change make-spike-elf to use the coreboot toolchain.

Change-Id: I81ced8c6e02b00a3835e3b42c9cf2669b1b2bd3e
Signed-off-by: Ronald G. Minnich <rminnich@gmail.com>
[jn: Added XGCC_BIN variable to avoid requiring the tools in $PATH]
Signed-off-by: Jonathan Neuschäfer <j.neuschaefer@gmx.net>
Reviewed-on: https://review.coreboot.org/16955
Tested-by: build bot (Jenkins)
1 file changed