xen/arm: Stringify the register name in sysreg read write macros

xen/arm: Stringify the register name in sysreg read write macros

The register name parameter in {READ,WRITE}_SYSREG{32,64}
macros is replaced as register name in mrs and msr assembly
instruction.

If this register name is macro indirection, the register
name is not replaced with designated macro. So replace the register
name with __stringify macro, which replaces register name
if it is macro

Signed-off-by: Vijaya Kumar K <Vijaya.Kumar@caviumnetworks.com>
Acked-by: Ian Campbell <ian.campbell@citrix.com>
Acked-by: Julien Grall <julien.grall@linaro.org>