linuxkpi: Move invalidate_mapping_pages() to <linux/pagemap.h>

[Why]
This is consistent with Linux.

[How]
The definition is moved from <linux/shmem_fs.h> to <linux/pagemap.h> and
the latter is included from the former. This is how it is done on Linux.

Prototypes are also expanded with argument names. I got a build failure
in the DRM 5.18 drivers because the compiler considered that the
pgoff_t argument was there twice.

Reviewed by: manu
Approved by: manu
Differential Revision: https://reviews.freebsd.org/D43018