powerpc/book3s64/radix: add debug message to give more details of vmemmap allocation

Add some extra vmemmap pr_debug message that will indicate the type of
vmemmap allocations.

For ex: with DAX vmemmap optimization we can find the below details:
[  187.166580] radix-mmu: PAGE_SIZE vmemmap mapping
[  187.166587] radix-mmu: PAGE_SIZE vmemmap mapping
[  187.166591] radix-mmu: Tail page reuse vmemmap mapping
[  187.166594] radix-mmu: Tail page reuse vmemmap mapping
[  187.166598] radix-mmu: Tail page reuse vmemmap mapping
[  187.166601] radix-mmu: Tail page reuse vmemmap mapping
[  187.166604] radix-mmu: Tail page reuse vmemmap mapping
[  187.166608] radix-mmu: Tail page reuse vmemmap mapping
[  187.166611] radix-mmu: Tail page reuse vmemmap mapping
[  187.166614] radix-mmu: Tail page reuse vmemmap mapping
[  187.166617] radix-mmu: Tail page reuse vmemmap mapping
[  187.166620] radix-mmu: Tail page reuse vmemmap mapping
[  187.166623] radix-mmu: Tail page reuse vmemmap mapping
[  187.166626] radix-mmu: Tail page reuse vmemmap mapping
[  187.166629] radix-mmu: Tail page reuse vmemmap mapping
[  187.166632] radix-mmu: Tail page reuse vmemmap mapping

And without vmemmap optimization
[  293.549931] radix-mmu: PMD_SIZE vmemmap mapping
[  293.549984] radix-mmu: PMD_SIZE vmemmap mapping
[  293.550032] radix-mmu: PMD_SIZE vmemmap mapping
[  293.550076] radix-mmu: PMD_SIZE vmemmap mapping
[  293.550117] radix-mmu: PMD_SIZE vmemmap mapping

Link: https://lkml.kernel.org/r/20230724190759.483013-14-aneesh.kumar@linux.ibm.comSigned-off-by: Aneesh Kumar K.V <aneesh.kumar@linux.ibm.com>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Christophe Leroy <christophe.leroy@csgroup.eu>
Cc: Dan Williams <dan.j.williams@intel.com>
Cc: Joao Martins <joao.m.martins@oracle.com>
Cc: Michael Ellerman <mpe@ellerman.id.au>
Cc: Mike Kravetz <mike.kravetz@oracle.com>
Cc: Muchun Song <muchun.song@linux.dev>
Cc: Nicholas Piggin <npiggin@gmail.com>
Cc: Oscar Salvador <osalvador@suse.de>
Cc: Will Deacon <will@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

arch/powerpc/mm/book3s64/radix_pgtable.c

@@ -1033,6 +1033,7 @@ static pte_t * __meminit radix__vmemmap_pte_populate(pmd_t *pmdp, unsigned long
 				p = vmemmap_alloc_block_buf(PAGE_SIZE, node, NULL);
 			if (!p)
 				return NULL;
+			pr_debug("PAGE_SIZE vmemmap mapping\n");
 		} else {
 			/*
 			 * When a PTE/PMD entry is freed from the init_mm
@@ -1045,6 +1046,7 @@ static pte_t * __meminit radix__vmemmap_pte_populate(pmd_t *pmdp, unsigned long
 			 */
 			get_page(reuse);
 			p = page_to_virt(reuse);
+			pr_debug("Tail page reuse vmemmap mapping\n");
 		}
 
 		VM_BUG_ON(!PAGE_ALIGNED(addr));
@@ -1154,6 +1156,7 @@ int __meminit radix__vmemmap_populate(unsigned long start, unsigned long end, in
 			p = vmemmap_alloc_block_buf(PMD_SIZE, node, altmap);
 			if (p) {
 				vmemmap_set_pmd(pmd, p, node, addr, next);
+				pr_debug("PMD_SIZE vmemmap mapping\n");
 				continue;
 			} else if (altmap) {
 				/*