advfs: Update dependencies of bs_bitfile_sets.h
advfs: Add missing dependency fot vm_page_t
advfs: Minor cleaning, group common includes together
advfs: Rename globally st_atime -> advfs_st_atime to fix clash with st_atime from sys/stat.h
advfs: Rename globally st_mtime -> advfs_st_mtime to fix clash with st_mtime from sys/stat.h