xshm: XSHM Configuration data handling

xshm: XSHM Configuration data handling

This patch implements the configuration handling:
- reception of gen-netlink requests from user-space.
- calculating address of where to put information in shared memory, i.e
  the offset of: IPC-TOC, channel-descriptors, read/write indexes for each
  directional channel, and data area of each channel.
- formatting of the shared memory area, so modem can read out configuration
  data.
- Creation of configuration data given to the XSHM drivers: xshm_chr and
  caif_xshm.

Signed-off-by: Sjur Brændeland <sjur.brandeland@stericsson.com>
Signed-off-by: Linus Walleij <linus.walleij@stericsson.com>