powerpc/8xx: Fix initial memory mapping

Commit cf209951 ("powerpc/8xx: Map linear memory with huge pages")
introduced an initial mapping of kernel TEXT using PAGE_KERNEL_TEXT,
but the pages that contain kernel TEXT may also contain kernel RODATA,
and depending on selected debug options PAGE_KERNEL_TEXT may be either
RWX or ROX. RODATA must be writable during init because it also
contains ro_after_init data.

So use PAGE_KERNEL_X instead to be sure it is RWX.

Fixes: cf209951 ("powerpc/8xx: Map linear memory with huge pages")
Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://msgid.link/dac7a828d8497c4548c91840575a706657baa4f1.1724173828.git.christophe.leroy@csgroup.eu

arch/powerpc/mm/nohash/8xx.c

@@ -150,11 +150,11 @@ unsigned long __init mmu_mapin_ram(unsigned long base, unsigned long top)
 
 	mmu_mapin_immr();
 
-	mmu_mapin_ram_chunk(0, boundary, PAGE_KERNEL_TEXT, true);
+	mmu_mapin_ram_chunk(0, boundary, PAGE_KERNEL_X, true);
 	if (debug_pagealloc_enabled_or_kfence()) {
 		top = boundary;
 	} else {
-		mmu_mapin_ram_chunk(boundary, einittext8, PAGE_KERNEL_TEXT, true);
+		mmu_mapin_ram_chunk(boundary, einittext8, PAGE_KERNEL_X, true);
 		mmu_mapin_ram_chunk(einittext8, top, PAGE_KERNEL, true);
 	}