/proc/cpuinfo should just print all the isa string as an information
instead of determining what is supported or not. ELF hwcap can be
used by the userspace to figure out that.

Simplify the isa string printing by removing the unsupported isa string
print and all related code.

The relevant discussion can be found at
http://lists.infradead.org/pipermail/linux-riscv/2019-September/006702.htmlSigned-off-by: Atish Patra <atish.patra@wdc.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Link: http://lists.infradead.org/pipermail/linux-riscv/2019-September/006702.htmlSigned-off-by: Paul Walmsley <paul.walmsley@sifive.com>