Xtensa: use asm-generic/fcntl.h

Commit fc4fb2ad

 "fixed" the Xtensa
asm/fcntl.h and in doing so ignored asm-generic/fcntl.h completely.
It turns out that it is now exactly the same as asm-generic/fcntl.h.

Signed-off-by: Stephen Rothwell <sfr@canb.auug.org.au>
Signed-off-by: Chris Zankel <zankel@tensilica.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>