xtensa: stop filling syscall array with sys_ni_syscall

arch/xtensa/kernel/syscalls/syscalltbl.sh fills missing syscall numbers
with sys_ni_syscall.

So, the generated arch/xtensa/include/generated/asm/syscall_table.h
has no hole.

Hence, the line:

  [0 ... __NR_syscalls - 1] = (syscall_t)&sys_ni_syscall,

is meaningless.

The number of generated __SYSCALL() macros is the same as __NR_syscalls
(this is 442 as of v5.11).

Hence, the array size, [__NR_syscalls] is unneeded.

The designated initializer, '[nr] =', is also unneeded.

This file does not need to know __NR_syscalls. Drop the unneeded
<asm/unistd.h> include directive.

Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
Message-Id: <20210301153656.363839-1-masahiroy@kernel.org>
Signed-off-by: Max Filippov <jcmvbkbc@gmail.com>