uapi linux/coda_psdev.h: move upc_req definition from uapi to kernel side headers

uapi linux/coda_psdev.h: move upc_req definition from uapi to kernel side headers

Only users of upc_req in kernel side fs/coda/psdev.c and
fs/coda/upcall.c already include linux/coda_psdev.h.

Suggested by Jan Harkes <jaharkes@cs.cmu.edu> in
  https://lore.kernel.org/lkml/20150531111913.GA23377@cs.cmu.edu/

Fixes these include/uapi/linux/coda_psdev.h compilation errors in userspace:

  linux/coda_psdev.h:12:19: error: field `uc_chain' has incomplete type
  struct list_head    uc_chain;
                   ^
  linux/coda_psdev.h:13:2: error: unknown type name `caddr_t'
  caddr_t             uc_data;
  ^
  linux/coda_psdev.h:14:2: error: unknown type name `u_short'
  u_short             uc_flags;
  ^
  linux/coda_psdev.h:15:2: error: unknown type name `u_short'
  u_short             uc_inSize;  /* Size is at most 5000 bytes */
  ^
  linux/coda_psdev.h:16:2: error: unknown type name `u_short'
  u_short             uc_outSize;
  ^
  linux/coda_psdev.h:17:2: error: unknown type name `u_short'
  u_short             uc_opcode;  /* copied from data to save lookup */
  ^
  linux/coda_psdev.h:19:2: error: unknown type name `wait_queue_head_t'
  wait_queue_head_t   uc_sleep;   /* process' wait queue */
  ^

Link: http://lkml.kernel.org/r/9f99f5ce6a0563d5266e6cf7aa9585aac2cae971.1558117389.git.jaharkes@cs.cmu.edu
Signed-off-by: Mikko Rapeli <mikko.rapeli@iki.fi>
Signed-off-by: Jan Harkes <jaharkes@cs.cmu.edu>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Colin Ian King <colin.king@canonical.com>
Cc: Dan Carpenter <dan.carpenter@oracle.com>
Cc: David Howells <dhowells@redhat.com>
Cc: Fabian Frederick <fabf@skynet.be>
Cc: Sam Protsenko <semen.protsenko@linaro.org>
Cc: Yann Droneaud <ydroneaud@opteya.com>
Cc: Zhouyang Jia <jiazhouyang09@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>