arm: libpayload: Add cache coherent DMA memory definition and management

This patch adds a mechanism to set aside a region of cache-coherent
(i.e. usually uncached) virtual memory, which can be used to communicate
with DMA devices without automatic cache snooping (common on ARM)
without the need of explicit flush/invalidation instructions in the
driver code.

This works by setting aside said region in the (board-specific) page
table setup, as exemplary done in this patch for the Snow, Pit and Kirby
boards. It uses a new mechanism for adding board-specific Coreboot table
entries to describe this region in an entry with the LB_DMA tag.

Libpayload's memory allocator is enhanced to be able to operate on
distinct types/regions of memory. It provides dma_malloc() and
dma_memalign() functions for use in drivers, which by default just
operate on the same heap as their traditional counterparts. However, if
the Coreboot table parsing code finds a CB_DMA section, further requests
through the dma_xxx() functions will return memory from the region
described therein instead.

BUG=chrome-os-partner:21969
TEST=Manual

Change-Id: Ia9c249249e936bbc3eb76e7b4822af2230ffb186
Signed-off-by: Julius Werner <jwerner@chromium.org>
Reviewed-on: https://chromium-review.googlesource.com/167155

payloads/libpayload/include/stdlib.h

@@ -112,6 +112,9 @@ void *calloc(size_t nmemb, size_t size);
 void *realloc(void *ptr, size_t size);
 void *memalign(size_t align, size_t size);
 #endif
+void init_dma_memory(void *start, u32 size);
+void *dma_malloc(size_t size);
+void *dma_memalign(size_t align, size_t size);
 /** @} */
 
 /**