MIPS: Let early memblock_alloc*() allocate memories bottom-up

After switched to NO_BOOTMEM, there are several boot failures. Some of
them have been fixed and some of them haven't. I find that many of them
are because of memory allocations are top-down, while the old behavior
is bottom-up. This patch let early memblock_alloc*() allocate memories
bottom-up to avoid some potential problems.

Signed-off-by: Huacai Chen <chenhc@lemote.com>
Signed-off-by: Paul Burton <paul.burton@mips.com>
Fixes: bcec54bf3118 ("mips: switch to NO_BOOTMEM")
Patchwork: https://patchwork.linux-mips.org/patch/21069/
References: https://patchwork.linux-mips.org/patch/21031/
Cc: Ralf Baechle <ralf@linux-mips.org>
Cc: James Hogan <james.hogan@mips.com>
Cc: Steven J . Hill <Steven.Hill@cavium.com>
Cc: linux-mips@linux-mips.org
Cc: Fuxin Zhang <zhangfx@lemote.com>
Cc: Zhangjin Wu <wuzhangjin@gmail.com>

arch/mips/kernel/setup.c

@@ -794,6 +794,7 @@ static void __init arch_mem_init(char **cmdline_p)
 
 	/* call board setup routine */
 	plat_mem_setup();
+	memblock_set_bottom_up(true);
 
 	/*
 	 * Make sure all kernel memory is in the maps.  The "UP" and

arch/mips/kernel/traps.c

@@ -2260,10 +2260,8 @@ void __init trap_init(void)
 		unsigned long size = 0x200 + VECTORSPACING*64;
 		phys_addr_t ebase_pa;
 
-		memblock_set_bottom_up(true);
 		ebase = (unsigned long)
 			memblock_alloc_from(size, 1 << fls(size), 0);
-		memblock_set_bottom_up(false);
 
 		/*
 		 * Try to ensure ebase resides in KSeg0 if possible.
@@ -2307,6 +2305,7 @@ void __init trap_init(void)
 	if (board_ebase_setup)
 		board_ebase_setup();
 	per_cpu_trap_init(true);
+	memblock_set_bottom_up(false);
 
 	/*
 	 * Copy the generic exception handlers to their final destination.