arch/mips: some variants need different gcc versions

arch/mips: some variants need different gcc versions

We use the conditions currently expressed in the gcc version choice.

We leave the musl vs mips64 conditions in gcc, because the "fault"
really is on gcc, which does not recognise the mips64+musl tuples,
so the fix lies within gcc, and the current conditions are fitting.

Signed-off-by: "Yann E. MORIN" <yann.morin.1998@free.fr>
Cc: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>