It seems I accidentally switched the guard on linux/elf-fdpic.h from #ifdef
__KERNEL__ to #ifndef __KERNEL__ when attempting to expand the guarded region
to cover the elf_fdpic_params struct when doing the UAPI split - with the
result that the struct became unavailable to kernel code.
Move incorrectly guarded bits back to the kernelspace header.
Whilst we're at it, the __KERNEL__ guards can be deleted as they're no longer
necessary.