arm64: Fix building error with 16KB pages and 36-bit VA

In such configuration, Linux uses only two pages of page tables and
__pud_populate() should not be used. However, the BUILD_BUG() triggers
since pud_sect() is still defined and the compiler cannot eliminate such
code, even though at run-time it should not be triggered. This patch
extends the #ifdef ARM64_64K_PAGES condition for pud_sect to include
PGTABLE_LEVELS < 3.

Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>

arch/arm64/include/asm/pgtable.h

@@ -395,7 +395,7 @@ extern pgprot_t phys_mem_access_prot(struct file *file, unsigned long pfn,
 #define pmd_sect(pmd)		((pmd_val(pmd) & PMD_TYPE_MASK) == \
 				 PMD_TYPE_SECT)
 
-#ifdef CONFIG_ARM64_64K_PAGES
+#if defined(CONFIG_ARM64_64K_PAGES) || CONFIG_PGTABLE_LEVELS < 3
 #define pud_sect(pud)		(0)
 #define pud_table(pud)		(1)
 #else