grub, syslinux, memtest: replace memtest to boot/

features.in/grub/cfg.in/90memtest_bios.cfg

 if [ "$grub_platform" = "pc" ]; then
-	menuentry $"Memory Test" --id 'memtest' {
-		linux16 /syslinux/memtest.bin
-	}
+  menuentry $"Memory Test" --id 'memtest' {
+    linux16 /boot/memtest.bin
+  }
 fi

features.in/memtest/stage1/scripts.d/02-memtest

 #!/bin/sh
 
-mkdir -p "$WORKDIR"/syslinux
+mkdir -p "$WORKDIR"/boot
 MEMTEST="$(find /boot/ -name 'memtest*' -print -quit)"
 # hdt wiki recommends adding .bin
 [ -z "$MEMTEST" ] ||
-	cp -f "$MEMTEST" "$WORKDIR"/syslinux/memtest.bin
+	cp -f "$MEMTEST" "$WORKDIR"/boot/memtest.bin

features.in/syslinux/cfg.in/90memtest.cfg

 label memtest
   menu label ^Memory Test
-  linux memtest.bin
+  linux /boot/memtest.bin