Documentation: vgaarbiter: Fix grammar

Documentation: vgaarbiter: Fix grammar

Correct grammar issues:

- Fix "co-exist" subject-verb agreement
- Correct plural form of "server" in context of more than one legacy
  devices
- Use passive mood for intro sentence of libpciaccess section

Signed-off-by: Pranav Tyagi <pranav.tyagi03@gmail.com>
Reviewed-by: Bagas Sanjaya <bagasdotme@gmail.com>
Link: https://lore.kernel.org/r/20250220164946.18007-1-pranav.tyagi03@gmail.com
[Bagas: massage commit message]
Signed-off-by: Bagas Sanjaya <bagasdotme@gmail.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20250318041249.20786-2-bagasdotme@gmail.com
Signed-off-by: Maxime Ripard <mripard@kernel.org>