tcg: Remove support for ia64 as host

We threatened to remove ia64 as host in v2.9.0.  Its time has now come.

There are still some usages of defined(__ia64__) throughout the source
code that would be triggered if one were to enable TCI on an ia64 host.
Leave those alone for now.

Signed-off-by: Richard Henderson <richard.henderson@linaro.org>