conf/machine/include: Set TUNE_CCARGS instead of TARGET_CC_ARCH
Since we're updating the tune file format, it makes sense to abstract
the compiler tune arguments at this point too. This means that should
these need to be overridden at any point, the original values can
still be obtained in a similar manner to the other TUNE* variables.
Whilst this isn't strictly necessary for any current need, its likely
good practise to standardise this behaviour.
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>
