util/crossgcc: Bump GMP version to 6.1.0

The previous official GMP release (6.0.0) contains a bug that
prevents compilation on ppc64el systems.  Increase version
to the latest version (6.1.0).

Bug details:

gcc build on ppc64el fails with:
(.text+0x4c): undefined reference to `BMOD_1_TO_MOD_1_THRESHOLD'

While I don't have an exact commit hash due to Hg use upstream,
a missing BMOD_1_TO_MOD_1_THRESHOLD define on ppc64el was quietly
fixed in Hg before the 6.1.0 release.

Change-Id: I1c05a1c194141db5f8522148c2e20e7558d34714
Signed-off-by: Timothy Pearson <tpearson@raptorengineeringinc.com>
Reviewed-on: https://review.coreboot.org/12811
Tested-by: build bot (Jenkins)
Reviewed-by: Paul Menzel <paulepanter@users.sourceforge.net>
Reviewed-by: Martin Roth <martinroth@google.com>
Reviewed-by: Ronald G. Minnich <rminnich@gmail.com>
diff --git a/util/crossgcc/sum/gmp-6.1.0.tar.bz2.cksum b/util/crossgcc/sum/gmp-6.1.0.tar.bz2.cksum
new file mode 100644
index 0000000..06db257
--- /dev/null
+++ b/util/crossgcc/sum/gmp-6.1.0.tar.bz2.cksum
@@ -0,0 +1 @@
+db38c7b67f8eea9f2e5b8a48d219165b2fdab11f  tarballs/gmp-6.1.0.tar.bz2