arm64: Correct __NR_compat_syscalls for bpf

Commit 97b56be1 (arm64: compat: Enable bpf syscall) made the
usual mistake of forgetting to update __NR_compat_syscalls. Due to this,
when el0_sync_compat calls el0_svc_naked, the test against sc_nr
(__NR_compat_syscalls) will fail, and we'll call ni_sys, returning
-ENOSYS to userspace.

This patch bumps __NR_compat_syscalls appropriately, enabling the use of
the bpf syscall from compat tasks.

Due to the reorganisation of unistd{,32}.h as part of commit
f3e5c847 (arm64: Add __NR_* definitions for compat syscalls) it
is not currently possible to include both headers and sanity-check the
value of __NR_compat_syscalls at build-time to prevent this from
happening again. Additional rework is required to make such niceties a
possibility.

Cc: Will Deacon <will.deacon@arm.com>
Acked-by: Catalin Marinas <catalin.marinas@arm.com>
Signed-off-by: Mark Rutland <mark.rutland@arm.com>
Signed-off-by: Will Deacon <will.deacon@arm.com>