iwlwifi: add tm commands for sram reading by dumpit

Create new testmode commands and attributes to suppot
sram data reading. Because the amount of sram data
may exceed single skb packet size. Using the nl80211
dump it funtion to deliver sram data to userspace.

- IWL_TM_CMD_APP2DEV_READ_SRAM
- IWL_TM_CMD_APP2DEV_DUMP_SRAM
- IWL_TM_ATTR_SRAM_ADDR
- IWL_TM_ATTR_SRAM_SIZE
- IWL_TM_ATTR_SRAM_DUMP

Signed-off-by: Kenny Hsu <kenny.hsu@intel.com>
Signed-off-by: Wey-Yi Guy <wey-yi.w.guy@intel.com>