Regarding the changes on /proc/cpuinfo for ISA strings

[Ruinland Tsai]

Hi Atish and all,

After the commit "a9b202606" introduced for Kernel v5.18,
the `/proc/cpuinfo` will longer print the full ISA string provided by DTB.

With the comment of that commit, it seems that the policy of `cpuinfo` has
changed to print only the extensions provided in the array 
"riscv_isa_ext_data" and those extensions must be properly enabled (by 
toggling corresponding Kconfig ?).

So we are wondering a few things and hope that you can enlighten us a 
little bit :

1. What is the policy on recieving vendor extensions ?
Hypothetically speaking, if a vendor submits a patch which simply adds an 
entry into `riscv_isa_ext_data[]` without revealing any detail, will that 
be acceptable ?

2. If a userspace program wishes to know the whole ISA string, is 
`/proc/device-tree` the last resort for them ? And if that's the case, 
what will the equivalent in the ACPI world since we have learnt that the 
RISC-V ACPI spec is now work in progress.

Cordially yours,
Ruinland ChuanTzu Tsai