arm64/kexec: Use consistent convention of initializing 'kxec_buf.mem' with KEXEC_BUF_MEM_UNKNOWN

With commit b6664ba4 ("s390, kexec_file: drop arch_kexec_mem_walk()"),
we introduced the KEXEC_BUF_MEM_UNKNOWN macro. If kexec_buf.mem is set
to this value, kexec_locate_mem_hole() will try to allocate free memory.

While other arch(s) like s390 and x86_64 already use this macro to
initialize kexec_buf.mem with, arm64 uses an equivalent value of 0.
Replace it with KEXEC_BUF_MEM_UNKNOWN, to keep the convention of
initializing 'kxec_buf.mem' consistent across various archs.

Cc: takahiro.akashi@linaro.org
Cc: james.morse@arm.com
Reviewed-by: Matthias Brugger <mbrugger@suse.com>
Signed-off-by: Bhupesh Sharma <bhsharma@redhat.com>
Signed-off-by: Will Deacon <will@kernel.org>

arch/arm64/kernel/kexec_image.c

@@ -84,7 +84,7 @@ static void *image_load(struct kimage *image,
 
 	kbuf.buffer = kernel;
 	kbuf.bufsz = kernel_len;
-	kbuf.mem = 0;
+	kbuf.mem = KEXEC_BUF_MEM_UNKNOWN;
 	kbuf.memsz = le64_to_cpu(h->image_size);
 	text_offset = le64_to_cpu(h->text_offset);
 	kbuf.buf_align = MIN_KIMG_ALIGN;

arch/arm64/kernel/machine_kexec_file.c

@@ -177,7 +177,7 @@ int load_other_segments(struct kimage *image,
 	if (initrd) {
 		kbuf.buffer = initrd;
 		kbuf.bufsz = initrd_len;
-		kbuf.mem = 0;
+		kbuf.mem = KEXEC_BUF_MEM_UNKNOWN;
 		kbuf.memsz = initrd_len;
 		kbuf.buf_align = 0;
 		/* within 1GB-aligned window of up to 32GB in size */
@@ -204,7 +204,7 @@ int load_other_segments(struct kimage *image,
 	dtb_len = fdt_totalsize(dtb);
 	kbuf.buffer = dtb;
 	kbuf.bufsz = dtb_len;
-	kbuf.mem = 0;
+	kbuf.mem = KEXEC_BUF_MEM_UNKNOWN;
 	kbuf.memsz = dtb_len;
 	/* not across 2MB boundary */
 	kbuf.buf_align = SZ_2M;