cmake: add check_arguments_... macro to facilitate function writing

Add a new zephyr_check_arguments_required_allow_empty() macro for
function argument validation.

Zephyr already has a zephyr_check_arguments_required() for checking
required arguments, like
zephyr_check_arguments_required(foo_func <prefix> FOO BAR)
which ensures that one of FOO or BAR are given in a call like:
foo_func(BAR val)

One limitation however, is that is some cases BAR may be allowed to be
empty, so that it's still possible to know if FOO or BAR were supplied.
In most case, BAR and FOO will have values following the keyword, like:
foo_func(BAR my_bar_val)
foo_func(FOO my_foo_val)

but in cases where `my_bar_val` is a variable which may be empty, like:
set(my_bar_val)
foo_func(BAR ${my_bar_val}) # (expands to: foo_func(BAR)

then BAR was actually supplied.
To support functions where such empty expansion is allowed, then a new
helper macro `zephyr_check_arguments_required_allow_empty()` has been
implemented, as to be able to distinguish `foo_func()` from
`foo_func(BAR)` when parsing arguments.

Signed-off-by: Torsten Rasmussen <Torsten.Rasmussen@nordicsemi.no>