Improved Acronym List in Glossary

Created by: sifferman

I added a few acronyms and fixed a couple typos. Here is the full changes list:

• Moved VLEN and XLEN so the list is now fully alphabetical
• Changed all occurrences of "lengh" to "length"
• Added
  • APU
  • AXI
  • BHT
  • BTB
  • CVA6
  • D$
  • DPI
  • EX
  • I$
  • MMU
  • NC
  • OoO
  • PMP
  • PTW
  • RAS
  • S-Mode
  • TLB
  • U-Mode