goarch.bbclass: use MACHINEOVERRIDES and simplify go_map_arm()
Per https://github.com/golang/go/wiki/GoArm we need to set GOARM when
cross building for ARMv5, ARMv6 and ARMv7. The current approach of
using TUNE_FEATURES can be error prone, as we can see today when
attempting to build for Cortex-A7 which results in GOARM=''.
Since the value of MACHINEOVERRIDES already consolidates the values of
TUNE_FEATURES into something more consistent we can use the overrides
mechanism to set GOARM, leaving just a little bit of logic in
go_map_arm() to trigger off the arch (basically target vs host)
for the setting of GOARM.
Signed-off-by: Mark Asselstine <mark.asselstine@windriver.com> Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>
