UCP/CORE: Check result md_map inside ucp_mem_map()

[dmitrygx]

What

Check result md_map inside ucp_mem_map() and report an error if it is empty.

Why ?

Memory handle registration/allocation should be considered as invalid, if no Memory Domains could be used to register memory.

How ?

1. Combine ucp_memh_create() and ucp_memh_init_uct_reg() to ucp_memh_reg() function.
2. After calling ucp_mem_alloc()/ucp_memh_reg() check memh->md_map == 0. If it is true, report an error and deallocate a created memory handle.

[dmitrygx]

@Artemy-Mellanox @brminich could you review pls?

[dmitrygx]

will be combined with #8552, because need to check md_map only for imported memhs