aarch64: rcpc3: Add FP load/store insns

aarch64: rcpc3: Add FP load/store insns

Along with the relevant unit-tests, this adds the following rcpc3
instructions:

  STL1  { <Vt>.D }[<index>], [<Xn|SP>]
  LDAP1 { <Vt>.D }[<index>], [<Xn|SP>]

  LDAPUR <Bt>, [<Xn|SP>{, #<simm>}]
  LDAPUR <Ht>, [<Xn|SP>{, #<simm>}]
  LDAPUR <St>, [<Xn|SP>{, #<simm>}]
  LDAPUR <Dt>, [<Xn|SP>{, #<simm>}]
  LDAPUR <Qt>, [<Xn|SP>{, #<simm>}]

  STLUR <Bt>, [<Xn|SP>{, #<simm>}]
  STLUR <Ht>, [<Xn|SP>{, #<simm>}]
  STLUR <St>, [<Xn|SP>{, #<simm>}]
  STLUR <Dt>, [<Xn|SP>{, #<simm>}]
  STLUR <Qt>, [<Xn|SP>{, #<simm>}]

with `#<simm>' taking on a signed 8-bit integer value in the range
[-256,255] and `index' the values 0 or 1.

Co-authored-by: Srinath Parvathaneni <srinath.parvathaneni@arm.com>