cvdso_call_time macro is very similar to cvdso_call macro.

Add a call_time argument to cvdso_call which is 0 by default
and set to 1 when using cvdso_call to call __c_kernel_time().

Return returned value as is with CR[SO] cleared when it is used
for time().
Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/837a260ad86fc1ce297a562c2117fd69be5f7b5c.1642782130.git.christophe.leroy@csgroup.eu