bnxt: Enforce PTP software freq adjustments only when in non-RTC mode

Currently driver performs software based frequency adjustments
when RTC capability is not discovered or when in shared PHC mode.
But there may be some old firmware versions that still support
hardware freq adjustments without RTC capability being exposed.
In this situation driver will use non-realtime mode even on single
host NICs.

Hence enforce software frequency adjustments only when running in
shared PHC mode. Make suitable changes for cyclecounter for the
same.

Signed-off-by: Pavan Chebbi <pavan.chebbi@broadcom.com>
Reviewed-by: Michael Chan <michael.chan@broadcom.com>
Acked-by: Vadim Fedorenko <vadim.fedorenko@linux.dev>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>