drivers/cmsis-dap: tidy up buffer access

Each one of CMSIS-DAP command handlers was responsible for setting
HID report number, which in case of USB bulk transport was not used
at all. The command had to be filled with 1 byte offset whereas
the response was read without an offset.

Introduce 'command' and 'response' pointers into struct cmsis_dap.
Use them for filling the command and read the response respectively.
CMSIS-DAP command parameter are now at positions as documented in
https://arm-software.github.io/CMSIS_5/DAP/html/group__DAP__Commands__gr.html


Adjust buffer allocation for HID and USB bulk transports.

While on it, use h_u32_to_le() and h_u16_to_le() instead of per-byte
writes.

Change-Id: Ib0808d6826ba0e254c1007ace8b743405536332a
Signed-off-by: Tomas Vanek <vanekt@fbl.cz>
Reviewed-on: http://openocd.zylin.com/6120


Reviewed-by: Adrian M Negreanu <adrian.negreanu@nxp.com>
Tested-by: jenkins
Reviewed-by: Tarek BOCHKATI <tarek.bouchkati@gmail.com>