doc: ti: am335x_evm: Minor general updates

- At this point there are a large number of Beaglebone boards, refer to
  them as a family rather than a growing list.
- Reword customization as we're largely Kconfig-oriented now.
- Remove the NOR section as the relevant defconfigs have long been
  removed and the general support was not updated.

Signed-off-by: Tom Rini <trini@konsulko.com>
1 file changed