rp2/mpnetworkport: Convert network task scheduling to use PendSV IRQ.

It is more reliable and scales better when more components need it.

Work done in collaboration with Graham Sanderson and Peter Harper.

Signed-off-by: Damien George <damien@micropython.org>

ports/rp2/CMakeLists.txt

@@ -111,6 +111,7 @@ set(MICROPY_SOURCE_PORT
     mphalport.c
     mpnetworkport.c
     mpthreadport.c
+    pendsv.c
     rp2_flash.c
     rp2_pio.c
     tusb_port.c
@@ -141,6 +142,7 @@ set(MICROPY_SOURCE_QSTR
 )
 
 set(PICO_SDK_COMPONENTS
+    cmsis_core
     hardware_adc
     hardware_base
     hardware_clocks