package/Makefile.in: fix ABI name for EABIhf targets

The current code to set ABI on ARM does the following:

ifeq ($(BR2_arm)$(BR2_armeb),y)
... set ABI without 'hf' suffix ...
else ifeq ($(BR2_ARM_EABIHF),y)
... set ABI with 'hf' suffix ...
endif

But since $(BR2_arm)$(BR2_armeb) will always be 'y' in the cases where
BR2_ARM_EABIHF is 'y', it means that the 'else' part of the condition
will never be used.

Fix this by appending 'hf' to the ABI variable when BR2_ARM_EABIHF is
selected.

[Peter: put EABIhf handling under arm/armeb conditional for consistency]
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Signed-off-by: Peter Korsgaard <jacmet@sunsite.dk>