gopsutil's cpu.Info() does not parse the 'cpu model' field from
/proc/cpuinfo, which is the only source of CPU model names on MIPS.
Add a fallback that reads /proc/cpuinfo directly and combines
'cpu model' (e.g. 'MIPS 1004Kc V2.15') with 'system type'
(e.g. 'MediaTek MT7621 ver:1 eco:3') for a complete identifier.
The fallback only triggers when gopsutil returns an empty ModelName,
so x86/ARM/other architectures are unaffected.
