buildroot

gdb: switch to 7.10 as the default version

7.11 is around, 7.10 has already seen a point release, so it's time to
make 7.10 the default version for gdb.

Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>