arm64/mm: Drop PMD_TABLE_BIT from pmd_trans_huge()

This changes pmd_trans_huge() to return true, when the pmd entry is either
a section mapping or an invalid but present entry made via pmd_mkinvalid()
thus containing PTE_PRESENT_INVALID. This just re-arranges existing checks
while also dropping redundant pmd_val().

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