CRIS: UAPI: fix elf.h export

CRIS userspace (uClibc for one) expects asm/elf.h to be exported but
this header appears to have gone missing at some point.  Move it to
uapi/ and export it.

Signed-off-by: Rabin Vincent <rabin@rab.in>
Signed-off-by: Jesper Nilsson <jesper.nilsson@axis.com>