Revert "elf: Relax MIPS' elf_check_arch() to accept EM_NANOMIPS too"

Per the "P32 Porting Guide" (rev 1.2) [1], chapter 2:

  p32 ABI Overview
  ----------------

  The Application Binary Interface, or ABI, is the set of rules
  that all binaries must follow in order to run on a nanoMIPS
  system. This includes, for example, object file format,
  instruction set, data layout, subroutine calling convention,
  and system call numbers. The ABI is one part of the mechanism
  that maintains binary compatibility across all nanoMIPS platforms.

  p32 improves on o32 to provide an ABI that is efficient in both
  code density and performance. p32 is required for the nanoMIPS
  architecture.

So far QEMU only support the MIPS o32 / n32 / n64 ABIs. The p32 ABI
is not implemented, therefore we can not run any nanoMIPS binary.

Revert commit f72541f3 ("elf: Relax MIPS' elf_check_arch() to
accept EM_NANOMIPS too").

See also the "ELF ABI Supplement" [2].

[1] http://codescape.mips.com/components/toolchain/nanomips/2019.03-01/docs/MIPS_nanoMIPS_p32_ABI_Porting_Guide_01_02_DN00184.pdf
[2] http://codescape.mips.com/components/toolchain/nanomips/2019.03-01/docs/MIPS_nanoMIPS_ABI_supplement_01_03_DN00179.pdf



Signed-off-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Message-Id: <20211101114800.2692157-1-f4bug@amsat.org>