aarch64: ADD FEAT_THE RCWCAS instructions.

aarch64: ADD FEAT_THE RCWCAS instructions.

This patch adds support for FEAT_THE doubleword and quadword instructions.
doubleword insturctions are enabled by "+the" flag whereas quadword
instructions are enabled on passing both "+the and +d128" flags.

Support for following sets of instructions is added in this patch.
Read check write compare and swap doubleword:
(rcwcas, rcwcasa, rcwcasal, rcwcasl)
Read check write compare and swap quadword:
(rcwcasp,rcwcaspa, rcwcaspal, rcwcaspl)
Read check write software compare and swap doubleword:
(rcwscas, rcwscasa, rcwscasal, rcwscasl)
Read check write software compare and swap quadword:
(rcwscasp, rcwscaspa, rcwscaspal, rcwscaspl)
Read check write atomic bit clear on doubleword:
(rcwclr, rcwclra, rcwclral, rcwclrl)
Read check write atomic bit clear on quadword:
(rcwclrp, rcwclrpa, rcwclrpal, rcwclrpl)
Read check write software atomic bit clear on doubleword:
(rcwsclr, rcwsclra, rcwsclral, rcwsclrl)
Read check write software atomic bit clear on quadword:
(rcwsclrp,rcwsclrpa, rcwsclrpal,rcwsclrpl)
Read check write atomic bit set on doubleword:
(rcwset,rcwseta, rcwsetal,rcwsetl)
Read check write atomic bit set on quadword:
(rcwsetp,rcwsetpa,rcwsetpal,rcwsetpl)
Read check write software atomic bit set on doubleword:
(rcwsset,rcwsseta,rcwssetal,rcwssetl)
Read check write software atomic bit set on quadword:
(rcwssetp,rcwssetpa,rcwssetpal,rcwssetpl)
Read check write swap doubleword:
(rcwswp,rcwswpa,rcwswpal,rcwswpl)
Read check write swap quadword:
(rcwswpp,rcwswppa, rcwswppal,rcwswppl)
Read check write software swap doubleword:
(rcwsswp,rcwsswpa,rcwsswpal,rcwsswpl)
Read check write software swap quadword:
(rcwsswpp,rcwsswppa,rcwsswppal,rcwsswppl)