meson: auto-enable etnaviv on arm, arc, mips and loongarch architectures

There is a Vivante GC1000 gpu in LS2K1000 and LS7A1000.

LS7A1000 is a bridge chip made by Loongson corporation
which act as north and/or south bridge of loongson's
desktop and server level processor. It is equivalent
to RS780E or something like that. In fact, the company
use RS780E as bridge of LS3A3000 at its early stage,
but as RS780E is out of stock long long time ago, the
company have to made one by themself. More details can
be read from its user manual[1].

This bridge chip typically use with LS3A3000, LS3A4000
and LS3A5000.

LS3A3000 is 4 core 1.45gHz mips64r2 compatible cpu.
LS3A4000 is 4 core 1.8gHz mips64r5 compatible cpu.
LS3A5000 is 4 core 2.5gHz loongarch cpu, the company
acclaim that loongarch a new archtecture with its
instruction set is released[2].

LS2K1000 is a double core 1.0Ghz mips64r2 compatible SoC[3].

we need to enable it to test and developing driver on above
listed archtecture.

[1] https://loongson.github.io/LoongArch-Documentation/Loongson-7A1000-usermanual-EN.html
[2] https://loongson.github.io/LoongArch-Documentation/Loongson-3A5000-usermanual-EN.html
[3] https://wiki.debian.org/InstallingDebianOn/Lemote/Loongson2K1000



Signed-off-by: Sui Jingfeng <15330273260@189.cn>

[Eric: rebase over meson changes, add ARM & ARC architectures, and drop
"experimental" from the description]
Signed-off-by: Eric Engestrom <eric@engestrom.ch>