[stm32] Place stack in SRAM by default on H7, add lbuild option

The DTCM is not DMA-capable on H7 devices. An lbuild option is added to
select the stack location between SRAM and DTCM.

src/modm/platform/core/stm32/idtcm.ld.in

@@ -31,7 +31,11 @@ SECTIONS
 %% set dtcm_section = "DTCM"
 %% endif
 
+%% if stack_in_dtcm
 {{ linker.section_stack(dtcm_section) }}
+%% else
+{{ linker.section_stack(cont_ram.cont_name|upper) }}
+%% endif
 
 %% if "dtcm" in cont_ram.cont_name
 {{ linker.section_ram(cont_ram.cont_name|upper, "FLASH", table_copy, table_zero,

src/modm/platform/core/stm32/module.lb

@@ -30,6 +30,15 @@ def prepare(module, options):
                 default="rom")
             )
 
+    if options[":target"].identifier.family == "h7":
+        module.add_option(
+            EnumerationOption(
+                name="stack_location",
+                description="SRAM (default) or DTCM (faster, but not DMA-capable)",
+                enumeration=["sram", "dtcm"],
+                default="sram")
+            )
+
     module.depends(":platform:cortex-m")
     return True
 
@@ -83,6 +92,7 @@ def build(env):
 
 
 def post_build(env):
+    target = env[":target"].identifier
     env.substitutions = env.query("::cortex-m:linkerscript")
     env.substitutions.update(env.query("::cortex-m:vector_table"))
     env.outbasepath = "modm/link"
@@ -100,5 +110,6 @@ def post_build(env):
                 linkerscript = "dccm.ld.in"
         elif memory["name"] == "dtcm":
             # Executable ITCM and DTCM (Tightly-Coupled Memory)
+            env.substitutions["stack_in_dtcm"] = env.get(":platform:core:stack_location", "dtcm") == "dtcm"
             linkerscript = "idtcm.ld.in"
     env.template(linkerscript, "linkerscript.ld")