linux-user/mips: Use P5600 as default CPU to run NaN2008 ELF binaries

linux-user/mips: Use P5600 as default CPU to run NaN2008 ELF binaries

Per the release 6.06 revision history:

 5.03 August 21, 2013

 • ABS2008 and NAN2008 fields of Table 5.7 “FCSR RegisterField
   Descriptions” were optional in release 3 and could be R/W,
   but as of release 5 are required, read-only, and preset by
   hardware.

The P5600 core implements the release 5, and has the ABS2008
and NAN2008 bits set in CP1_fcr31. Therefore it is able to run
ELF binaries compiled with EF_MIPS_NAN2008, such the CIP United
Debian NaN2008 distribution:
http://repo.oss.cipunited.com/mipsel-nan2008/README.txt

In order to run such compiled binaries, select by default the
P5600 core when the ELF 'MIPS_NAN2008' flag is set.

Reported-by: Jiaxun Yang <jiaxun.yang@flygoat.com>
Signed-off-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Acked-by: Laurent Vivier <laurent@vivier.eu>
Message-Id: <20230327162444.388-1-philmd@linaro.org>