Most of this file is only used inside of libfc, so move it to where it is
actually used, with only fc_fill_fc_hdr() left inside of the header.

Link: https://lore.kernel.org/r/20201026160705.3706396-1-arnd@kernel.orgReported-by: Nkernel test robot <lkp@intel.com>
Signed-off-by: NArnd Bergmann <arnd@arndb.de>
Signed-off-by: NMartin K. Petersen <martin.petersen@oracle.com>