riscv: Fix 32b kernel build with CONFIG_DEBUG_VIRTUAL=y

Declare kernel_virt_addr for 32b kernel since it is used in
__phys_addr_symbol defined when CONFIG_DEBUG_VIRTUAL is set.

Fixes: 2bfc6cd ("riscv: Move kernel mapping outside of linear mapping")
Signed-off-by: Alexandre Ghiti <alex@ghiti.fr>
Signed-off-by: Palmer Dabbelt <palmerdabbelt@google.com>

arch/riscv/include/asm/page.h

@@ -106,9 +106,9 @@ extern unsigned long pfn_base;
 #define ARCH_PFN_OFFSET		(PAGE_OFFSET >> PAGE_SHIFT)
 #endif /* CONFIG_MMU */
 
-#ifdef CONFIG_64BIT
 extern unsigned long kernel_virt_addr;
 
+#ifdef CONFIG_64BIT
 #define linear_mapping_pa_to_va(x)	((void *)((unsigned long)(x) + va_pa_offset))
 #ifdef CONFIG_XIP_KERNEL
 #define kernel_mapping_pa_to_va(y)	({						\