T9014: Makefile: cap TEST_MEM at 4GB on arm64/aarch64

QEMU's virt board cannot place guest RAM above the 4GiB boundary when
the vCPU only exposes a 32-bit IPA range, aborting with "Addressing
limited to 32 bits, but memory exceeds it by ... bytes". Force
TEST_MEM to 4 on arm64/aarch64 regardless of host RAM to avoid it.

Author: c-po

Makefile

@@ -12,8 +12,11 @@ UEFI_FLAG := $(if $(filter arm64 aarch64,$(ARCH)),--uefi,)
 TEST_CPUS := $(shell printf '%s\n' "$$(nproc)" 4 | sort -n | head -n1)
 
 # Common memory size (GB) for QEMU test targets: 8GB if the host has at
-# least 10GB of RAM, otherwise 4GB
-TEST_MEM := $(shell awk '/MemTotal/{if ($$2/1024/1024 >= 10) print 8; else print 4}' /proc/meminfo)
+# least 10GB of RAM, otherwise 4GB. Capped at 4GB on arm64/aarch64
+# regardless of host RAM - QEMU's virt board cannot place guest RAM above
+# the 4GiB boundary when the vCPU only exposes a 32-bit IPA range, and
+# exceeding it aborts with "Addressing limited to 32 bits".
+TEST_MEM := $(if $(filter arm64 aarch64,$(ARCH)),4,$(shell awk '/MemTotal/{if ($$2/1024/1024 >= 10) print 8; else print 4}' /proc/meminfo))
 
 # Test targets forward extra CLI arguments (e.g. `make test -- --match foo`)
 # to their scripts via $(MAKECMDGOALS). Those extra words are also goals as