targets: rename qemu target to cortex-m-qemu

The target is intended to emulate the Cortex-M, not to be a generic QEMU
target.

targets/cortex-m-qemu.json

@@ -8,7 +8,7 @@
 	],
 	"linkerscript": "targets/lm3s6965.ld",
 	"extra-files": [
-		"targets/qemu.s"
+		"targets/cortex-m-qemu.s"
 	],
 	"emulator": ["qemu-system-arm", "-machine", "lm3s6965evb", "-semihosting", "-nographic", "-kernel"]
 }

targets/cortex-m-qemu.s

@@ -1,5 +1,5 @@
 // Generic Cortex-M interrupt vector.
-// This vector is used by the QEMU target.
+// This vector is used by the Cortex-M QEMU target.
 
 .syntax unified