bpf: Pass a pointer to arch_bpf_timed_may_goto()

arch_bpf_timed_may_goto() gets the offset of count and timestamp in the
stack frame in BPF_REG_AX. Arch code adds the frame pointer to it, and
calls bpf_check_timed_may_goto() with the result. On arm64, riscv,
loongarch, powerpc and s390 the asm function does it. On x86-64 the JIT
does it, because the frame pointer is in another register when the prog has
a private stack.

The next patch moves count and timestamp out of the stack frame. So pass
the pointer in BPF_REG_AX, and let the verifier emit the addition:

  before                           after

  r12 = -16                        r12 = r10
  call arch_bpf_timed_may_goto     r12 += -16
                                   call arch_bpf_timed_may_goto

The JITs know which register r10 is. The asm functions have a move in place
of the addition, and the special case in the x86-64 JIT goes away.

These insns run when the count is used up: in each 65535th iteration. The
cost of an iteration does not change.

Three tests have the insns of may_goto in them. Update them.

Tested on x86-64, and on arm64 and s390 in QEMU. riscv, loongarch and
powerpc are compile tested only.

Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Link: https://patch.msgid.link/20261031215543.682284-7-alexei.starovoitov@gmail.com

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