bnxt_en: Add PTP .getcrosststamp() interface to get device/host times

bnxt_en: Add PTP .getcrosststamp() interface to get device/host times

.getcrosststamp() helps the applications to obtain a snapshot of
device and host time almost taken at the same time. This function
will report PCIe PTM device and host times to any application using
the ioctl PTP_SYS_OFFSET_PRECISE. The device time from the HW is
48-bit and needs to be converted to 64-bit.

Reviewed-by: Somnath Kotur <somnath.kotur@broadcom.com>
Reviewed-by: Vadim Fedorenko <vadim.fedorenko@linux.dev>
Signed-off-by: Pavan Chebbi <pavan.chebbi@broadcom.com>
Signed-off-by: Michael Chan <michael.chan@broadcom.com>
Link: https://patch.msgid.link/20260108183521.215610-3-michael.chan@broadcom.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>