lscpu: RISC-V: Print ISA information in summary

lscpu: RISC-V: Print ISA information in summary

The ISA information for RISC-V is important for understanding the
different extensions supported by the CPU. Print the ISA information in
the summary, with the Base ISA and single-letter extensions at the
beginning, followed by multi-letter extensions sorted in alphabetical
order. The information is the same as the cpuinfo information, except
that underscores are replaced by spaces and multi-letter extensions are
simply sorted instead of following any ISA string ordering rule.

The sample output below shows the difference between cpuinfo and lscpu.

cpuinfo output:
isa             : rv64imafdch_zicbom_zicboz_zicntr_zicsr_zifencei_zihintntl_zihintpause_zihpm_zawrs_zfa_zba_zbb_zbc_zbs_smaia_ssaia_sstc

lscpu output:
ISA:                rv64imafdch smaia ssaia sstc zawrs zba zbb zbc zbs zfa zicbom zicboz zicntr zicsr zifencei zihintntl zihintpause zihpm

Signed-off-by: Sunil V L <sunilvl@ventanamicro.com>