Implement r_io_submap_set_from and r_io_submap_set_to (siol eternal)

[condret]

Description

Motivation

When inserting new submaps into a RIOBank, adjusting the boundaries of existing submaps is necessary, to ensure that submaps don't intersect.

Task

Implement r_io_submap_set_from and r_io_submap_set_to in libr/io/io_submap.c on siol_eternal branch:

R_API bool r_io_submap_set_from(RIOSubmap *sm, const ut64 from);
R_API bool r_io_submap_set_to(RIOSubmap *sm, const ut64 to);

Both functions shall return false, if sm is NULL or changing boundaries would result in negative interval size.
Else return true

[arv-77]

@condret , do the functions also have to change the values of sm->itv.addr and sm->itv.size?

[condret]

@arvindmuralie77 yes, sorry I didn't see your comment until now, I just implemented them