bpf, mips: Implement R4000 workarounds for JIT

For R4000 erratas around multiplication and division instructions,
as our use of those instructions are always followed by mflo/mfhi
instructions, the only issue we need care is

"MIPS R4000PC/SC Errata, Processor Revision 2.2 and 3.0" Errata 28:
"A double-word or a variable shift may give an incorrect result if
executed while an integer multiplication is in progress."

We just emit a mfhi $0 to ensure the operation is completed after
every multiplication instruction according to workaround suggestion
in the document.

Signed-off-by: Jiaxun Yang <[email protected]>
Signed-off-by: Daniel Borkmann <[email protected]>
Reviewed-by: Philippe Mathieu-Daudé <[email protected]>
Acked-by: Johan Almbladh <[email protected]>
Link: https://lore.kernel.org/bpf/[email protected]

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