intel: adsp: fix firmware image in IMR overwriting

The IMR is used by the firmware to hold its own copy for hot-booting
and for an "L3 heap," used for slow large allocations like loadable
libraries. The beginning of the L3 heap is currently hard-coded and
now the firmware has grown too large to fit into the dedicated area
so that it gets overwritten by heap allocations. This is a critical
bug that needs an urgent solution, for which we increase the offset,
but a real fix must calculate the L3 heap offset automatically.

BugLink: https://github.com/thesofproject/sof/issues/9308


Signed-off-by: Guennadi Liakhovetski <guennadi.liakhovetski@linux.intel.com>