linux-user: SPARC "rd %tick" can be used by user application

linux-user: SPARC "rd %tick" can be used by user application

we have the same problem decribed in 7d6b1daedd
("linux-user, ppc: mftbl can be used by user application")
for ppc in the case of sparc.

When we use an application trying to resolve a name, it hangs in

    0x00000000ff5dd40c:  rd  %tick, %o5
    0x00000000ff5dd410:  srlx  %o5, 0x20, %o4
    0x00000000ff5dd414:  btst  %o5, %g4
    0x00000000ff5dd418:  be  %icc, 0xff5dd40c

because %tick is staying at 0.

As QEMU_CLOCK_VIRTUAL is not available in linux-user mode,
simply use cpu_get_host_ticks() instead.

Signed-off-by: Laurent Vivier <laurent@vivier.eu>
Reviewed-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Message-Id: <20180528194812.31216-1-laurent@vivier.eu>