ath10k: refactor firmware images to struct ath10k_fw_components

To make it easier to share ath10k_core_fetch_board_data_api_n() with testmode.c
refactor all firmware components to struct ath10k_fw_components. This structure
will hold firmware related files, for example firmware-N.bin and board-N.bin.

For firmware-N.bin create a new struct ath10k_fw_file which contains the actual
firmware image as well as the parsed data from the image.

Modify ath10k_core_start() to take struct ath10k_fw_components() as an argument
which makes it possible in following patches to drop some ugly hacks from
testmode.c.

Signed-off-by: Kalle Valo <kvalo@qca.qualcomm.com>