tune-core2: Only add the current ARCH to PACKAGE_EXTRA_ARCHS

tune-core2: Only add the current ARCH to PACKAGE_EXTRA_ARCHS

Inherit the PACKAGE_EXTRA_ARCHS from i586 and only explicitly add core2
here.

(From OE-Core rev: 2a10d570560c37eb1d23cf853c0e541bc08a2878)

Signed-off-by: Darren Hart <dvhart@linux.intel.com>
Cc: Richard Purdie <richard.purdie@linuxfoundation.org>
Cc: Paul Eggleton <paul.eggleton@intel.com>
Cc: Tom Zanussi <tom.zanussi@intel.com>
Cc: Nitin Kamble <nitin.a.kamble@intel.com>
Cc: Mark Hatle <mark.hatle@windriver.com>
Cc: Bruce Ashfield <bruce.ashfield@windriver.com>
Cc: Martin Jansa <martin.jansa@gmail.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>