arm64: Kconfig: Re-jig CONFIG options for 52-bit VA

Enabling 52-bit VAs for userspace is pretty confusing, since it requires
you to select "48-bit" virtual addressing in the Kconfig.

Rework the logic so that 52-bit user virtual addressing is advertised in
the "Virtual address space size" choice, along with some help text to
describe its interaction with Pointer Authentication. The EXPERT-only
option to force all user mappings to the 52-bit range is then made
available immediately below the VA size selection.

Signed-off-by: Will Deacon <will.deacon@arm.com>

arch/arm64/kernel/head.S

@@ -318,7 +318,7 @@ __create_page_tables:
 	adrp	x0, idmap_pg_dir
 	adrp	x3, __idmap_text_start		// __pa(__idmap_text_start)
 
-#ifdef CONFIG_ARM64_52BIT_VA
+#ifdef CONFIG_ARM64_USER_VA_BITS_52
 	mrs_s	x6, SYS_ID_AA64MMFR2_EL1
 	and	x6, x6, #(0xf << ID_AA64MMFR2_LVA_SHIFT)
 	mov	x5, #52
@@ -800,7 +800,7 @@ ENTRY(__enable_mmu)
 ENDPROC(__enable_mmu)
 
 ENTRY(__cpu_secondary_check52bitva)
-#ifdef CONFIG_ARM64_52BIT_VA
+#ifdef CONFIG_ARM64_USER_VA_BITS_52
 	ldr_l	x0, vabits_user
 	cmp	x0, #52
 	b.ne	2f

arch/arm64/kernel/smp.c

@@ -139,7 +139,7 @@ int __cpu_up(unsigned int cpu, struct task_struct *idle)
 		if (!cpu_online(cpu)) {
 			pr_crit("CPU%u: failed to come online\n", cpu);
 
-			if (IS_ENABLED(CONFIG_ARM64_52BIT_VA) && va52mismatch)
+			if (IS_ENABLED(CONFIG_ARM64_USER_VA_BITS_52) && va52mismatch)
 				pr_crit("CPU%u: does not support 52-bit VAs\n", cpu);
 
 			ret = -EIO;