rtos: introduce rtos_put_gdb_reg()

and use it in rtos_get_gdb_reg() after get_thread_reg_value()
to allow passing long register value without hackish use of
struct rtos_reg.

Fixes: 9123: rtos: Dynamically allocate memory for RTOS registers
Link: https://review.openocd.org/c/openocd/+/9123
Change-Id: I30a51dcca60d67a0f01aa957c9c6076f266b5758
Signed-off-by: Tomas Vanek <vanekt@fbl.cz>
Reviewed-on: https://review.openocd.org/c/openocd/+/9135
Tested-by: jenkins
Reviewed-by: Evgeniy Naydanov <evgeniy.naydanov@syntacore.com>

src/rtos/rtos.h

@@ -53,8 +53,6 @@ struct rtos_reg {
 	uint32_t number;
 	uint32_t size;
 	uint8_t value[16];
-	/* WARNING: rtos_get_gdb_reg() relies on the fact that value is the last
-	 * element of this struct. Any new fields should be added *before* value. */
 };
 
 struct rtos_type {