xen/arm64: Use __flush_dcache_area instead of __flush_dcache_all

xen/arm64: Use __flush_dcache_area instead of __flush_dcache_all

When booting with EFI, __flush_dcache_all does not correctly flush data.
According to Mark Rutland, __flush_dcache_all is not guaranteed to push
data to the PoC if there is a system-level cache as it uses Set/Way
operations.  Therefore, this patch switchs to use the "__flush_dcache_area"
mechanism, which is coppied from Linux.
Add flushing of FDT in addition to Xen text/data.
Remove now unused __flush_dcache_all and related helper functions.
Invalidate the instruction tlb before turning on paging
later on when starting Xen in EL2.

Signed-off-by: Suravee Suthikulpanit <Suravee.Suthikulpanit@amd.com>
Signed-off-by: Roy Franz <roy.franz@linaro.org>
Acked-by: Ian Campbell <ian.campbell@citrix.com>