intel_adsp: ace30: mm: Set write permissions during memory mapping

The adsp_mm_save_context function was previously mapping memory without
explicitly setting write permissions, which could lead to a "store
prohibited" exception when attempting to write to the memory. This patch
adds the K_MEM_PERM_RW flag to the arch_mem_map call to ensure that the
memory is mapped with write permissions.

This change resolves the issue of accessing memory without the necessary
permissions, preventing potential exceptions and ensuring correct memory
operations. The issue was found when running the firmware on a
simulation with the MMU enabled.

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