pico_flash: Support FreeRTOS Static Allocation

[SConaway]

Fixes #2120

Allows pico_flash to use FreeRTOS static allocation as currently static-only builds fail without this change.

[kilograham]

Seems like this might be a nicer alternative

    TaskHandle_t xTaskCreateStaticAffinitySet( TaskFunction_t pxTaskCode,
                                               const char * const pcName, /*lint !e971 Unqualified char types are allowed for strings and single characters only. */
                                               const uint32_t ulStackDepth,
                                               void * const pvParameters,
                                               UBaseType_t uxPriority,
                                               StackType_t * const puxStackBuffer,
                                               StaticTask_t * const pxTaskBuffer,
                                               UBaseType_t uxCoreAffinityMask ) PRIVILEGED_FUNCTION;

[SConaway]

One thing I want to get your thoughts on (and sorry for the couple days of delay here): would it be better to default to static allocation and only switch to dynamic if static allocation isn't enabled?

[SConaway]

Seems like this might be a nicer alternative

    TaskHandle_t xTaskCreateStaticAffinitySet( TaskFunction_t pxTaskCode,
                                               const char * const pcName, /*lint !e971 Unqualified char types are allowed for strings and single characters only. */
                                               const uint32_t ulStackDepth,
                                               void * const pvParameters,
                                               UBaseType_t uxPriority,
                                               StackType_t * const puxStackBuffer,
                                               StaticTask_t * const pxTaskBuffer,
                                               UBaseType_t uxCoreAffinityMask ) PRIVILEGED_FUNCTION;

For some reason I skipped that — I can switch to it and let you know if it compiles. Unfortunately I don't really have any way to make sure that things still work besides compiling.

[kilograham]

compiling is better than me as I don't have a config with this setup, so would have to make one

[kilograham]

OK, so this isn't ideal as it will likely crash if flash_safe_execute() is called from both cores concurrently in this case.. I am approving anyway, because

a) This does compile and likely works correctly when not doing that
b) That use case is probably unlikely
c) Arguably the existing implementation is not very robust in that regard, so I will open a separate issue