Arm backend: Set default allocation pool to 20MB

This is making memory fit on more targets. The intention is for this
is to be easier to change from the run.sh flow and then this value
will probably be bumped back to the bigger value out of the box again
to make large model testing more convenient.

Signed-off-by: Zingo Andersen <[email protected]>
Change-Id: Id0e5f0d453bddc8e8fb0db65a4fd72bc7c1671ea

Author: zingo

examples/arm/executor_runner/arm_executor_runner.cpp

@@ -85,7 +85,7 @@ using executorch::runtime::TensorInfo;
  * availible memory.
  */
 #ifndef ET_ARM_BAREMETAL_METHOD_ALLOCATOR_POOL_SIZE
-#define ET_ARM_BAREMETAL_METHOD_ALLOCATOR_POOL_SIZE (60 * 1024 * 1024)
+#define ET_ARM_BAREMETAL_METHOD_ALLOCATOR_POOL_SIZE (20 * 1024 * 1024)
 #endif
 const size_t method_allocation_pool_size =
     ET_ARM_BAREMETAL_METHOD_ALLOCATOR_POOL_SIZE;