Refactor miner_thread to be common code for any kind of device

This expands on the device API, by taking the actual main thread out of the
device's code, and calling the API only for specific tasks. This brings
various changes that were made to the GPU thread code into the CPU miner.
It also fixes a bug where shares found on old GPU work were discarded when
it switched to a new work.

miner.h

@@ -210,6 +210,7 @@ struct gpu_adl {
 
 struct cgpu_info;
 struct thr_info;
+struct work;
 
 struct device_api {
 	char*name;
@@ -222,7 +223,13 @@ struct device_api {
 	void (*get_statline)(char*, struct cgpu_info*);
 
 	// Thread-specific functions
-	void (*thread_start)(struct thr_info*);
+	bool (*thread_prepare)(struct thr_info*);
+	uint64_t (*can_limit_work)(struct thr_info*);
+	bool (*thread_init)(struct thr_info*);
+	void (*free_work)(struct thr_info*, struct work*);
+	bool (*prepare_work)(struct thr_info*, struct work*);
+	uint64_t (*scanhash)(struct thr_info*, struct work*, uint64_t);
+	void (*thread_shutdown)(struct thr_info*);
 };
 
 struct cgpu_info {
@@ -278,6 +285,7 @@ struct thr_info {
 	pthread_t	pth;
 	struct thread_q	*q;
 	struct cgpu_info *cgpu;
+	void *cgpu_data;
 	struct timeval last;
 	struct timeval sick;