wlcore: access the firmware memory via debugfs

Applications running in the user space needs access to the
memory of the chip. Examples of such access
- read/write global variables
- access to firmware log
- dump memory after firmware panic event

Arbitrary 4-bytes aligned location can be accessed by
read/write file wlcore/mem

[Check return value of wlcore_raw_read/write and wlcore_set_partition
calls as required by the recent IO changes. -- Luca]

Signed-off-by: Arkady Miasnikov <a-miasnikov@ti.com>
Signed-off-by: Luciano Coelho <coelho@ti.com>