sfc: Cope with permissions enforcement added to firmware for SR-IOV

* Accept EPERM in some simple cases, the following cases are handled:
1) efx_mcdi_read_assertion()
Unprivileged PCI functions aren't allowed to GET_ASSERTS.
We return success as it's up to the primary PF to deal with asserts.
2) efx_mcdi_mon_probe() in efx_ef10_probe()
Unprivileged PCI functions aren't allowed to read sensor info, and
worrying about sensor data is the primary PF's job.
3) phy_op->reconfigure() in efx_init_port() and efx_reset_up()
Unprivileged functions aren't allowed to MC_CMD_SET_LINK, they just have
to accept the settings (including flow-control, which is what
efx_init_port() is worried about) they've been given.
4) Fallback to GET_WORKAROUNDS in efx_ef10_probe()
Unprivileged PCI functions aren't allowed to set workarounds. So if
efx_mcdi_set_workaround() fails EPERM, use efx_mcdi_get_workarounds()
to find out if workaround_35388 is enabled.
5) If DRV_ATTACH gets EPERM, try without specifying fw-variant
Unprivileged PCI functions have to use a FIRMWARE_ID of 0xffffffff
(MC_CMD_FW_DONT_CARE).
6) Don't try to exit_assertion unless one had fired
Previously we called efx_mcdi_exit_assertion even if
efx_mcdi_read_assertion had received MC_CMD_GET_ASSERTS_FLAGS_NO_FAILS.
This is unnecessary, and the resulting MC_CMD_REBOOT, even if the
AFTER_ASSERTION flag made it a no-op, would fail EPERM for unprivileged
PCI functions.
So make efx_mcdi_read_assertion return whether an assert happened, and only
call efx_mcdi_exit_assertion if it has.

Signed-off-by: Shradha Shah <sshah@solarflare.com>
Signed-off-by: David S. Miller <davem@davemloft.net>