[PATCH, AArch64] Re-organize aarch64_classify_symbol

[Marcus Shawcroft]

This patch re-organizes the implementation of aarch64_classify_symbol in 
preparation for add tiny absolute memory model support.

Regressed aarch64-none-elf, applied.
/Marcus

2013-05-29  Chris Schlumberger-Socha <chris.schlumberger-so...@arm.com>
            Marcus Shawcroft  <marcus.shawcr...@arm.com>

        * config/aarch64/aarch64.c (aarch64_classify_symbol): Remove comment.
        Refactor if/switch.  Replace gcc_assert with if.