mwifiex: cleanup ioctl wait queue and abstraction layer

1) remove mwifiex_alloc_fill_wait_queue() and
mwifiex_request_ioctl()
2) avoid dynamic allocation of wait queue
3) remove unnecessary mwifiex_error_code macros that
were used mainly by the wait queue status code
4) remove some abstraction functions
5) split mwifiex_prepare_cmd() to mwifiex_send_cmd_async()
and mwifiex_send_sync() to handle asynchronous and
synchronous commands respectively

Signed-off-by: Amitkumar Karwar <akarwar@marvell.com>
Signed-off-by: Bing Zhao <bzhao@marvell.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>