interface: define TMS sequence command

For support of SWD we need to be able to clock out special bit
sequences over TMS or SWDIO.  Create this as a generic operation,
not yet called by anything, which is split as usual into:

 - upper level abstraction ... here, jtag_add_tms_seq();
 - midlayer implementation logic hooking that to the lowlevel code;
 - lowlevel minidriver operation ... here, interface_add_tms_seq();
 - message type for request queue, here JTAG_TMS.

This is done slightly differently than other operations: there's a flag
saying whether the interface driver supports this request.  (In fact a
flag *word* so upper layers can learn about other capabilities too ...
for example, supporting SWD operations.)

That approach (flag) lets this method *eventually* be used to eliminate
pathmove() and statemove() support from most adapter drivers, by moving
all that logic into the mid-layer and increasing uniformity between the
various drivers.  (Which will in turn reduce subtle bugginess.)

Signed-off-by: David Brownell <dbrownell@users.sourceforge.net>

src/jtag/jtag.h

@@ -575,6 +575,8 @@ tap_state_t jtag_get_end_state(void);
 
 void jtag_add_sleep(uint32_t us);
 
+int jtag_add_tms_seq(unsigned nbits, const uint8_t *seq, enum tap_state t);
+
 /**
  * Function jtag_add_clocks
  * first checks that the state in which the clocks are to be issued is
@@ -693,7 +695,7 @@ int jtag_error_clear(void);
 /**
  * Return true if it's safe for a background polling task to access the
  * JTAG scan chain.  Polling may be explicitly disallowed, and is also
- * unsafe while nTRST is active or the JTAG clock is gated off.,
+ * unsafe while nTRST is active or the JTAG clock is gated off.
  */
 bool is_jtag_poll_safe(void);