Also update comments and assertions in io.h:
- EF10 does not have a general BIU collector and does not have the
  bug affecting TIMER_COMMAND_REG[0] on Falcon/Siena
- The WPTR field moved within RX_DESC_UPD_REG and TX_DESC_UPD_REG.
  Adjust efx_writed_page() accordingly
Signed-off-by: Ben Hutchings <bhutchings@solarflare.com>