qtnfmac: cleanup alignment in firmware communication protocol

Make sure that all elements in QLINK protocol message are aligned to
4 bytes. For this purpose add necessary amount of padding bytes to
each message. Besides, add padding for non-aligned variable length
fields, e.g. SSID, so that the first byte of the next variable length
element is aligned. to 4 bytes. Finally, introduce TLV parsing helpers
to reduce boilerplate TLV parsing code.

Signed-off-by: Igor Mitsyanko <igor.mitsyanko.os@quantenna.com>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>