database: ensure frame rate is enabled when limiting it.

Some cameras default to automatic frame rate mode when power-cycled.
This makes the acquire period limitation ineffective, as the parameter
is ignored by the camera firmware.

Enforce manual frame rate setting at IOC start-up when limiting frame
rate. Note that the overwritten record already contains `PINI=YES` to
write this to hardware on `iocInit`.

Fixes: d5caf77 ("database: add option to limit camera frame rate.")

CameraApp/Db/limits.db

@@ -1,3 +1,7 @@
+record(bo, "$(P)$(R)FrameRateEnable") {
+   field(VAL, 1)
+}
+
 record(ao, "$(P)$(R)AcquirePeriod") {
    field(DRVL, "$(ACQUIRE_PERIOD_DRVL=0)")
    field(DRVH, "inf")