arm64: vdso: Remove redundant calls to flush_dcache_page()

arm64: vdso: Remove redundant calls to flush_dcache_page()

flush_dcache_page() ensures that the 'PG_dcache_clean' flag for its
'page' argument is clear so that cache maintenance will be performed
if the page is mapped into userspace with execute permissions.

Newly allocated pages have this flag clear, so there is no need to call
flush_dcache_page() for the compat vdso or signal pages. Remove the
redundant calls.

Signed-off-by: Will Deacon <will@kernel.org>
Reviewed-by: Vincenzo Frascino <vincenzo.frascino@arm.com>
Link: https://lore.kernel.org/r/20210318170738.7756-3-will@kernel.org
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>