package/pkg-meson: fix meson cpu_family format

meson requires a custom cpu_family format
https://mesonbuild.com/Reference-tables.html#cpu-families



Signed-off-by: James Hilliard <james.hilliard1@gmail.com>
Reviewed-by: Peter Seiderer <ps.report@gmx.net>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>