Retrieval of genomic position by using biomaRt package
BiomaRt cannot do that I'm afraid. There is an Ensembl REST API endpoint that will get you the genomic location of protein coordinates. It needs an Ensembl peptide ID an input though, so you could use the xref endpoint first to get that. There's a bit of sample code in R on those pages, you could use that to script together if you've got a list of these.