refactor flashing code into flash.h, so we can share it between platforms

client/flash.h

@@ -0,0 +1,15 @@
+struct partition {
+	int start;
+	int end;
+	int precious;
+	const char *name;
+};
+
+void FlushPrevious(int translate);
+void GotByte(uint32_t where, uint8_t which, int start_addr, int end_addr, int translate);
+unsigned int EnterFlashState(void);
+int PrepareFlash(struct partition *p, const char *filename, unsigned int state);
+int find_next_area(const char *str, int *offset, int *length);
+
+#define PHYSICAL_FLASH_START 0x100000
+void do_flash(char **argv);