target/i386: Split out do_fsave, do_frstor, do_fxsave, do_fxrstor

target/i386: Split out do_fsave, do_frstor, do_fxsave, do_fxrstor

The helper_* functions must use GETPC() to unwind from TCG.
The cpu_x86_* functions cannot, and directly calling the
helper_* functions is a bug.  Split out new functions that
perform the work and can be used by both.

Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
Reviewed-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Reviewed-by: Claudio Fontana <cfontana@suse.de>
Tested-by: Claudio Fontana <cfontana@suse.de>
Reviewed-by: Alex Bennée <alex.bennee@linaro.org>
Message-Id: <20210322132800.7470-4-cfontana@suse.de>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>