nimble/ll: Add common setting for SCA

Currently we have two separate SCA settings: actual SCA as ppm value and
enumerated one based on ranges of SCA value. This means user needs to
update both values and they ideally should be in sync.

To make our life easier, we can just have single BLE_LL_SCA setting to
provide ppm value and enumerated one can be easily determined at build
time.

porting/npl/riot/include/syscfg/syscfg.h

@@ -980,6 +980,11 @@
 #define MYNEWT_VAL_BLE_LL_RNG_BUFSIZE (32)
 #endif
 
+/* Value copied from BLE_LL_OUR_SCA */
+#ifndef MYNEWT_VAL_BLE_LL_SCA
+#define MYNEWT_VAL_BLE_LL_SCA (60)
+#endif
+
 #ifndef MYNEWT_VAL_BLE_LL_SCHED_AUX_CHAIN_MAFS_DELAY
 #define MYNEWT_VAL_BLE_LL_SCHED_AUX_CHAIN_MAFS_DELAY (0)
 #endif