common/multicall: Increase debugability for bad hypercalls

common/multicall: Increase debugability for bad hypercalls

While investigating an issue (in a new codepath I'd introduced, as it turns
out), leaving interrupts disabled manifested as a subsequent op in the
multicall failing a check_lock() test.

The codepath would have hit the ASSERT_NOT_IN_ATOMIC on the return-to-guest
path, had it not hit the check_lock() first.

Call ASSERT_NOT_IN_ATOMIC() after each operation in the multicall, to make
failures more obvious.

Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
Reviewed-by: George Dunlap <george.dunlap@citrix.com>
Reviewed-by: Wei Liu <wei.liu2@citrix.com>
Release-acked-by: Julien Grall <julien.grall@linaro.org>