arm64/mm: Drop TCR_SMP_FLAGS

Earlier TCR_SMP_FLAGS gets conditionally set as TCR_SHARED with CONFIG_SMP.
Currently CONFIG_SMP is always enabled on arm64 platforms, hence drop this
indirection via TCR_SMP_FLAGS and instead always directly use TCR_SHARED.

Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Will Deacon <will@kernel.org>
Cc: Ryan Roberts <ryan.roberts@arm.com>
Cc: linux-arm-kernel@lists.infradead.org
Cc: linux-kernel@vger.kernel.org
Signed-off-by: Anshuman Khandual <anshuman.khandual@arm.com>