Merge the directive-eabi_attribute.s and directive-eabi_attribute-2.s tests.

test/MC/ARM/directive-eabi_attribute.s had gotten out-of-sync with
test/MC/ARM/directive-eabi_attribute-2.s. The former tests the encoding of
build attributes in object files, and the latter the encoding in assembly
files. Since both these tests need to be updated at the same time, it makes
sense to combine them into a single test. The object file encodings are being
checked against the ouput of -arm-attributes rather than by direct byte
comparisons which makes for easier reading.

Change-Id: I0075de506ae5626fb2fa235383fe5ce6a65a15a9