Combine CCSRs with CSRs

[jasonyu1996]

Currently we have CSRs and CCSRs and separate sets of instructions to manipulate them. This is good but it becomes confusing when some CCSRs also accept integer values. We should consider just combining those two.

[jasonyu1996]

CHERI also has separate CCSRs (they call them special capability registers). Let's not touch this part for now but leave this issue open for the future.