boards: qemu: leon3: pass -m 1G to match DTS SRAM size

The qemu_leon3 DTS declares 1GB of SRAM (reg = <0x40000000 0x40000000>)
but the QEMU command line never specified a -m option, so QEMU used its
default of 128MB.  This mismatch was silently tolerated until now because
nothing validated the heap's end marker beyond physical RAM.

When CONFIG_COMMON_LIBC_MALLOC_ARENA_SIZE=-1 (the default), the malloc
heap claims the entire declared SRAM (~1GB).  The heap end marker chunk
is written at ~1GB offset from the heap base, well beyond QEMU's 128MB
of physical RAM.  Those writes are silently lost, leaving the end
marker's LEFT_SIZE field as zero.

Commit bec6349 ("lib: heap: introduce SYS_HEAP_HARDENING tiered
Kconfig") made bidirectional size round-trip checks the default when
CONFIG_ASSERT=y (MODERATE level).  The check left_chunk(right_chunk(c))
reads back the end marker's LEFT_SIZE and detects the zero value,
triggering "heap corruption (free chunk linkage)" across many unrelated
tests on this board.

Add -m 1G to the QEMU flags so the emulated RAM matches the declared
DTS size, consistent with how other QEMU boards (arc, riscv32, x86)
already specify their memory.

Signed-off-by: Nicolas Pitre <npitre@baylibre.com>

Author: Nicolas Pitre

boards/qemu/leon3/board.cmake

@@ -8,6 +8,7 @@ set(QEMU_CPU_TYPE_${ARCH} leon3)
 set(QEMU_FLAGS_${ARCH}
   -nographic
   -machine leon3_generic
+  -m 1G
   -icount auto
   )
 board_set_debugger_ifnset(qemu)