Initialize timer for us_ticker at startup

This avoids a stack overflow if sleep is called for the first time from
the idle thread (which by default has a fairly small stack, and which is
already fairly deep by the time it calls into the usticker adapter)

Author: Kyle Kearney

targets/TARGET_Cypress/TARGET_PSOC6/mbed_overrides.c

@@ -22,6 +22,7 @@
 #include "cybsp_api_core.h"
 #include "mbed_power_mgmt.h"
 #include "rtos_idle.h"
+#include "us_ticker_api.h"
 
 #if defined(COMPONENT_SPM_MAILBOX)
 void mailbox_init(void);
@@ -83,6 +84,11 @@ void mbed_sdk_init(void)
 #if !defined(TARGET_PSA)
     /* Set up the device based on configurator selections */
     cybsp_init();
+    /*
+     * Init the us Ticker here to avoid imposing on the limited stack space of the idle thread.
+     * This also allows the first call to sleep to occur faster.
+     */
+    us_ticker_init();
 #endif
 
     /* Enable global interrupts (disabled in CM4 startup assembly) */