libertas: GSPI device patch performance

[Mok Keith]

Hi all,

For the patch for GSPI devices, do we really need to create another
kernel thread for sending spi command. Since doing so, we need to
memcpy all the data from host to card, and it reduces performance. Can
we just send the command directly in host_to_card function, I believe
the comment that if_spi_host_to_card can't sleep is wrong. Since
hw_host_to_card is called by a kernel thread (lbs_thread) in main.c.

For interrupt event, we can just do a scheduled work to read the event cause.

Keith Mok