Support more risc-v extensions

[ziyao233]

Add support for zfa, zfh, zfhmin, zicsr and zifencei

tested on qemu-user version 8.2.1

$ qemu-riscv64 ./test
i = 1
m = 1
a = 1
f = 1
d = 1
c = 1
zfa = 1
zfh = 1
zfhmin = 1
zicsr = 1
zifencei = 1

[nihui]

capitalize Z ?

[ziyao233]

capitalize Z ?

is it really necessary? Lower cases match the other part's style better and ISA strings for gcc also contain lower cases only.

[nihui]

https://gcc.gnu.org/onlinedocs/gcc/RISC-V-Options.html
Ah ha, that's true
I don't remember what document uses a capital Z, it may be old.

[nihui]

Thanks for your contribution !