xtensa: minimize use of PLATFORM_DEFAULT_MEM_{ADDR,SIZE}

Now that the kernel load address and KSEG physical base address have
their own Kconfig symbols PLATFORM_DEFAULT_MEM seems redundant. It makes
little sense to use it in MMU configurations instead of KSEG_PADDR.
In noMMU configurations there's no explicit KSEG, so it's still useful
for the early cache initialization and definition of ARCH_PFN_OFFSET,
which affects mem_map size.

- limit it to noMMU; MMU variants have XCHAL_KSEG_PADDR and
  XCHAL_KSEG_SIZE;
- don't use it to define TASK_SIZE or MAX_LOW_PFN: first doesn't make
  any difference in noMMU, second is meaningless as there's no high
  memory;
- don't add default physical memory region: memory layout should come
  from the DT, bootloader tags, or memmap= command line parameter.

Signed-off-by: Max Filippov <jcmvbkbc@gmail.com>

arch/xtensa/kernel/setup.c

@@ -188,7 +188,6 @@ static int __init parse_bootparam(const bp_tag_t* tag)
 }
 
 #ifdef CONFIG_OF
-bool __initdata dt_memory_scan = false;
 
 #if !XCHAL_HAVE_PTP_MMU || XCHAL_HAVE_SPANNING_WAY
 unsigned long xtensa_kio_paddr = XCHAL_KIO_DEFAULT_PADDR;
@@ -228,9 +227,6 @@ static int __init xtensa_dt_io_area(unsigned long node, const char *uname,
 
 void __init early_init_dt_add_memory_arch(u64 base, u64 size)
 {
-	if (!dt_memory_scan)
-		return;
-
 	size &= PAGE_MASK;
 	add_sysmem_bank(base, base + size);
 }
@@ -242,9 +238,6 @@ void * __init early_init_dt_alloc_memory_arch(u64 size, u64 align)
 
 void __init early_init_devtree(void *params)
 {
-	if (sysmem.nr_banks == 0)
-		dt_memory_scan = true;
-
 	early_init_dt_scan(params);
 	of_scan_flat_dt(xtensa_dt_io_area, NULL);
 
@@ -278,12 +271,6 @@ void __init init_arch(bp_tag_t *bp_start)
 	early_init_devtree(dtb_start);
 #endif
 
-	if (sysmem.nr_banks == 0) {
-		add_sysmem_bank(PLATFORM_DEFAULT_MEM_START,
-				PLATFORM_DEFAULT_MEM_START +
-				PLATFORM_DEFAULT_MEM_SIZE);
-	}
-
 #ifdef CONFIG_CMDLINE_BOOL
 	if (!command_line[0])
 		strlcpy(command_line, default_command_line, COMMAND_LINE_SIZE);