tty: serial: bcm63xx: Update the Kconfig help text

Remove incorrect "bcm963xx_uart" module name; add a list of known users;
tweak grammar/indentation/capitalization.

Signed-off-by: Kevin Cernekee <cernekee@gmail.com>
Acked-by: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>