riscv: mm: fix wrong phys_ram_base value for RV64

Currently, if 64BIT and !XIP_KERNEL, the phys_ram_base is always 0,
no matter the real start of dram reported by memblock is.

Fixes: 6d7f91d9 ("riscv: Get rid of CONFIG_PHYS_RAM_BASE in kernel physical address conversion")
Signed-off-by: Jisheng Zhang <jszhang@kernel.org>
Reviewed-by: Alexandre Ghiti <alex@ghiti.fr>
Cc: stable@vger.kernel.org
Signed-off-by: Palmer Dabbelt <palmer@rivosinc.com>

arch/riscv/mm/init.c

@@ -187,10 +187,10 @@ static void __init setup_bootmem(void)
 
 
 	phys_ram_end = memblock_end_of_DRAM();
-#ifndef CONFIG_64BIT
 #ifndef CONFIG_XIP_KERNEL
 	phys_ram_base = memblock_start_of_DRAM();
 #endif
+#ifndef CONFIG_64BIT
 	/*
 	 * memblock allocator is not aware of the fact that last 4K bytes of
 	 * the addressable memory can not be mapped because of IS_ERR_VALUE