arch/arm: use EABIhf by default with VFP

Set EABIhf as the default target ABI for the ARM processors that have or
may have a VFP unit, since this ABI is the most efficient in that case.
Of course, EABI can still be selected manually if needed.

[Peter: only default to EABIHF when we are sure the CPU has a VFP]
Signed-off-by: Benoît Thébaudeau <benoit.thebaudeau.dev@gmail.com>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>