Fix alsa/sound/*.h for external programs

Fix alsa/sound/*.h for external programs

The recent update of sound/*.h to sync with the latest Linus uapi
files broke the build of alsa-tools programs.  These files used to be
a modified version of Linux sound/* header files, so that they could
be built without Linux headers.  The special prefix like __user and
other things were worked around there.

We may do that again, but a better approach is to fix those things in
Linux kernel uapi side, while we keep the minimal workaround in
alsa-lib such as the __u16 and co type definitions.

This patch is such an attempt, namely:
- Keep the original $LINUX/uapi/sound/*.h in include/sound/uapi
  directory
- The "fixes" are applied to some uapi headers, so that they don't
  contain Linux-specific prefix and use of opaque struct like
  snd_ctl_elem_id
- The uapi headers are included indirectly from include/sound/*.h
- Some headers have inclusion of type_compat.h for the Linux variable
  types and prefixes
- type_compat.h tries to use <linux/types.h> when __linux__ is
  defined, instead of the own conflicting definitions

The last type might need a bit more adjustment depending on the
compiler, but it can be fixed locally without disturbing else.

Signed-off-by: Takashi Iwai <tiwai@suse.de>