sfc: mark some unexported symbols as static

sfc: mark some unexported symbols as static

BugLink: https://bugs.launchpad.net/bugs/1836635
efx_default_channel_want_txqs() is only used in efx.c, while
 efx_ptp_want_txqs() and efx_ptp_channel_type (a struct) are only used
 in ptp.c.  In all cases these symbols should be static.

Fixes: 2935e3c38228 ("sfc: on 8000 series use TX queues for TX timestamps")
Signed-off-by: Fengguang Wu <fengguang.wu@intel.com>
[ecree@solarflare.com: rewrote commit message]
Signed-off-by: Edward Cree <ecree@solarflare.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
(cherry picked from commit e7345ba352d15c88cf9d8698a6f5bff9c25670eb)
Signed-off-by: Mauricio Faria de Oliveira <mfo@canonical.com>
Acked-by: Stefan Bader <stefan.bader@canonical.com>
Acked-by: Kleber Sacilotto de Souza <kleber.souza@canonical.com>
Signed-off-by: Kleber Sacilotto de Souza <kleber.souza@canonical.com>