Debug transition from LLC to SPM

[CyrilKoe]

Disabling the LLC can cause deadlock upon AXI reads.

These read request are routed to the hit_miss_detect but spm_lock blocks the lookup. We need to make sure that spm_lock is asserted only when there are not anymore requests inside the LLC.

The following code would break before this fix.

void llc_disable() {
    *reg32(&__base_llc, AXI_LLC_CFG_SPM_LOW_REG_OFFSET ) = 0xffffffff;
    *reg32(&__base_llc, AXI_LLC_CFG_SPM_HIGH_REG_OFFSET) = 0xffffffff;
    *reg32(&__base_llc, AXI_LLC_CFG_FLUSH_LOW_REG_OFFSET ) = 0xffffffff;
    *reg32(&__base_llc, AXI_LLC_CFG_FLUSH_HIGH_REG_OFFSET) = 0xffffffff;
    fence();
    // Stress the LLC using the icache
    fencei();
    // Disable the LLC
    *reg32(&__base_llc, AXI_LLC_COMMIT_CFG_REG_OFFSET) = 0x1;
    fence();
}