sunxi; Move spl HEAP to DRAM

u-boot does not call mem_malloc_init() until after dram has been setup, so
instead of wasting precious SRAM, simply but the HEAP in DRAM (just below
the BSS segment).

While at it change its size from 2 kB to 512 kB (same size as BSS) as we've
plenty of space in DRAM

Signed-off-by: Hans de Goede <hdegoede@redhat.com>
sunxi: remove READ_TIMER macro

Marek Vasut requested that this be removed during upstream review.

Since the inverting behaviour is a bit subtle I have decided to make this a
function rather than simply inlining the readl() at each of the users.

Signed-off-by: Ian Campbell <ijc@hellion.org.uk>
Signed-off-by: Hans de Goede <hdegoede@redhat.com>
sunxi: Change default bootm_szie to 0x10000000

We've boards which only have 256M of RAM, so using a default bootm_size
of 512M does not seem like a good idea.

Signed-off-by: Hans de Goede <hdegoede@redhat.com>