xtensa: add missing system calls to the syscall table

Add the following system calls to the syscall table:

fallocate
sendmmsg
umount2
syncfs
epoll_create1
inotify_init1
signalfd4
dup3
pipe2
timerfd_create
timerfd_settime
timerfd_gettime
eventfd2
preadv
pwritev
fanotify_init
fanotify_mark
process_vm_readv
process_vm_writev
name_to_handle_at
open_by_handle_at
sync_file_range
perf_event_open
rt_tgsigqueueinfo
clock_adjtime
prlimit64
kcmp

Note that we have to use the 'sys_sync_file_range2' version, so that
the 64-bit arguments are aligned correctly to the argument registers.

Signed-off-by: Chris Zankel <chris@zankel.net>