Add coverage for the recently added usercopy checks for vmalloc and
folios, via USERCOPY_VMALLOC and USERCOPY_FOLIO respectively.

Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Matthew Wilcox (Oracle) <willy@infradead.org>
Cc: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Kees Cook <keescook@chromium.org>