Move RISC-V specific typedefs to riscv.h

[ideapark]

No description provided.

[echtwerner]

Why your are moving the typedefs to riscv.h ?

I want to emphasize the importance of leaving comments on PRs. They provide valuable insights and guidance to both contributors and reviewers."

[ideapark]

Because the defined type pde_t are specific to riscv architecture,
and there is a defined type pte_t already in riscv.h, and those two
should be close to each other, since they are all riscv virtual memory
related.

Besides, types.h should be used as alias C standard types to compiler
level friendly shorter type names.