headers: don't depend on errno.h being available

These headers follow the pattern:

| #if CONFIG_IS_ENABLED(FANCY_FEATURE)
|   void foo(void);
| #else
|   static inline void foo(void) { return -ENOSYS; }
| #endif

In the #else path ENOSYS is used, however linux/errno.h is not included.
If errno.h has not been included already the compiler errors out even
if the inline function is not referenced.

Make those headers self contained.

Signed-off-by: Max Krummenacher <max.krummenacher@toradex.com>
Reviewed-by: Francesco Dolcini <francesco.dolcini@toradex.com>
Reviewed-by: Tom Rini <trini@konsulko.com>