soc: intel_adsp: ace: Ensure TLB entry for HW registers during power-down

This commit addresses an issue on platforms with an MMU where a
LoadStoreTLBMissCause exception occurs when accessing hardware registers
during the power-down process. The exception arises when attempting to
access the IPC register after HPSRAM has been powered down, leading to a
double exception: LoadStoreTLBMissCause followed by
InstrPIFDataErrorCause.

To resolve this, we preload the IPC register before shutting down
LPSRAM. This change prevents the double exception by ensuring that the
page table entries are correctly managed in the TLB before HPSRAM is
powered down and allowing the power-down sequence to complete
successfully.

Signed-off-by: Tomasz Leman <tomasz.m.leman@intel.com>