Clean-up entire document for consistency and better structure

This patch does following clean-ups in the entire asciidoc:
1. Ensure all lines don't extend beyond 80 characters
2. Have "Function: ", "Function Listing", and "Extension: "
   sub-sections under each section for each SBI extension
3. Fix attributes of all tables so that tables columns are sized
   based on required space
4. Use all upercase letters for RISC-V CSR fields and instructions
5. Use all lowercase letters for RISC-V CSR and register names
6. The document title should specify current version

Signed-off-by: Anup Patel <[email protected]>
Reviewed-by: Atish Patra <[email protected]>