For different devices, the mailbox flow between software and firmware is
different. There are several mailbox commands in the txgbe driver, but only
txgbe_hic_sr_read() was changed to use the new flow.
It leads to other mailbox commands timeout for Amber-Lite devices, which
is required to use the new flow. So this patch fills in the missing part.
For the sake of code tidy, txgbe_hic_sr_read() should change to use the
locked function txgbe_host_interface_command(), and this function could
be change to pointer in struct txgbe_mbx_info for different devices.