[merge] branch 'heapswitch'

This picks up the major work of allowing multiple heap implementations
and enable dlmalloc as an alternate heap to the simple existing one
(now called 'miniheap').

Also added a novm page allocator for memory management on systems too small
or missing an mmu to have a vm. Not much more than a simple bitmap allocator
that the heap pulls from. Allows for other heaps and/or users of physical
memory to coexist and span multiple banks of memory.

target/stm32746g-eval2/rules.mk

@@ -8,13 +8,9 @@ PLATFORM := stm32f7xx
 
 SDRAM_SIZE := 0x02000000
 SDRAM_BASE := 0xc0000000
-LCD_M_SIZE := 0x0012c000
 EXT_SRAM_BASE := 0x68000000
 EXT_SRAM_SIZE := 0x00200000
 
-HEAP_START := 0xc012c000
-HEAP_SIZE  := 0x01ed4000
-
 GLOBAL_DEFINES += \
     ENABLE_UART1=1 \
     ENABLE_SDRAM=1 \
@@ -23,10 +19,6 @@ GLOBAL_DEFINES += \
     EXT_SRAM_BASE=$(EXT_SRAM_BASE) \
     EXT_SRAM_SIZE=$(EXT_SRAM_SIZE) \
     ENABLE_EXT_SRAM=1 \
-\
-    WITH_STATIC_HEAP=1 \
-    HEAP_START=$(HEAP_START) \
-    HEAP_LEN=$(HEAP_SIZE) \
 \
     PKTBUF_POOL_SIZE=16