Use RELAXED ieee754 mode for Loongson-3 as 3A 4000 is 2008-only

Use RELAXED ieee754 mode for Loongson-3 as 3A 4000 is 2008-only

Forwarded: not-needed

There are 2 mode of value of IEEE NaN hardcoded by CPU.
Currently, our mipsel/mips64el port is in so-called lagacy mode.
Loongson 3A 4000 is set as the so-called 2008 mode.

To make Debian workable on Loongson 3A 4000, we need set the kerenl in
RELAXED mode.

https://web.archive.org/web/20180830093617/https://dmz-portal.mips.com/wiki/MIPS_ABI_-_NaN_Interlinking

[bwh: Update for addition of EMULATED mode in 6.11]

Gbp-Pq: Topic debian
Gbp-Pq: Name mips-ieee754-relaxed.patch