machine: Use cortexa17-neon as default tune for rk3288.inc
machine: Use cortexa17-neon as default tune for rk3288.inc

Support for this tune is now supported in yocto 1.9. As it comes
with gcc 5, we also need to require gcc 5.2 and minimal compiler
version.

Signed-off-by: Romain Perier <b3f268131c5a6ec066690d62d0a6c5c2b0bbcd85@gmail.com>
Reviewed-by: Trevor Woerner <8835777cd84fba3d7873eabbbe1f2de2d3f25b00@gmail.com>

twoerner/meta-rockchip-twoerner,hizukiayaka/meta-rockchip,hizukiayaka/meta-rockchip,hizukiayaka/meta-rockchip,twoerner/meta-rockchip-twoerner