net/sfc/base: import libefx base

net/sfc/base: import libefx base

libefx is a platform-independent library to implement drivers
for Solarflare network adapters. It provides unified adapter
family independent interface (if possible).

Driver must provide efsys.h header which defines options
(EFSYS_OPT_*) to be used and macros/functions to allocate
memory, read/write DMA-mapped memory, read/write PCI BAR
space, locks, barriers etc.

efx.h and efx_types.h provide external interfaces intended
to be used by drivers. Other header files are internal.

From Solarflare Communications Inc.

Signed-off-by: Andrew Rybchenko <arybchenko@solarflare.com>
Reviewed-by: Ferruh Yigit <ferruh.yigit@intel.com>