Subsys: Logging: Functions purely to avoid compiling error affects test coverage

[mengxianglinx]

Describe the bug
For function "void z_impl_z_log_string_from_user(uint32_t src_level_val, const char *str)", it be called neither in user space nor non-user space.
And for z_vrfy_z_log_hexdump_from_user, log_from_user, log_generic_from_user, log_hexdump_from_user defined for non-user space (line 1124-1170 in log_cor.c) are never called.
They must be there for reasons, but these functions affects test coverage.
Actually, the logic of defining these functions need refactor ,basically there is no reason to "do_some_thing_from_user" in non-user space.

[github-actions]

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