Don't include sysemu/tcg.h if it is not necessary

This header only defines the tcg_allowed variable and the tcg_enabled()
function - which are not required in many files that include this
header. Drop the #include statement there.

Signed-off-by: Thomas Huth <thuth@redhat.com>
Reviewed-by: Markus Armbruster <armbru@redhat.com>
Message-Id: <20220315144107.1012530-1-thuth@redhat.com>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>