arm64: vdso: simplify arch_vdso_type ifdeffery

Currently we have some ifdeffery to determine the number of elements in
enum arch_vdso_type as VDSO_TYPES, rather that the usual pattern of
having the enum define this:

| enum foo_type {
|         FOO_TYPE_A,
|         FOO_TYPE_B,
| #ifdef CONFIG_C
|         FOO_TYPE_C,
| #endif
|         NR_FOO_TYPES
| }

... however, given we only use this number to size the vdso_lookup[]
array, this is redundant anyway as the compiler can automatically size
the array to fit all defined elements.

So let's remove the VDSO_TYPES to simplify the code.

At the same time, let's use designated initializers for the array
elements so that these are guarnateed to be at the expected indices,
regardless of how we modify the structure. For clariy the redundant
explicit initialization of the enum elements is dropped.

There should be no functional change as a result of this patch.

Signed-off-by: Mark Rutland <mark.rutland@arm.com>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Vincenzo Frascino <vincenzo.frascino@arm.com>
Cc: Will Deacon <will@kernel.org>
Link: https://lore.kernel.org/r/20200428164921.41641-3-mark.rutland@arm.com
Signed-off-by: Will Deacon <will@kernel.org>

arch/arm64/kernel/vdso.c

@@ -35,16 +35,11 @@ extern char vdso32_start[], vdso32_end[];
 
 /* vdso_lookup arch_index */
 enum arch_vdso_type {
-	ARM64_VDSO = 0,
+	ARM64_VDSO,
 #ifdef CONFIG_COMPAT_VDSO
-	ARM64_VDSO32 = 1,
+	ARM64_VDSO32,
 #endif /* CONFIG_COMPAT_VDSO */
 };
-#ifdef CONFIG_COMPAT_VDSO
-#define VDSO_TYPES		(ARM64_VDSO32 + 1)
-#else
-#define VDSO_TYPES		(ARM64_VDSO + 1)
-#endif /* CONFIG_COMPAT_VDSO */
 
 struct __vdso_abi {
 	const char *name;
@@ -57,14 +52,14 @@ struct __vdso_abi {
 	struct vm_special_mapping *cm;
 };
 
-static struct __vdso_abi vdso_lookup[VDSO_TYPES] __ro_after_init = {
-	{
+static struct __vdso_abi vdso_lookup[] __ro_after_init = {
+	[ARM64_VDSO] = {
 		.name = "vdso",
 		.vdso_code_start = vdso_start,
 		.vdso_code_end = vdso_end,
 	},
 #ifdef CONFIG_COMPAT_VDSO
-	{
+	[ARM64_VDSO32] = {
 		.name = "vdso32",
 		.vdso_code_start = vdso32_start,
 		.vdso_code_end = vdso32_end,