accel/amdxdna: Add AIE4 work buffer initialization

accel/amdxdna: Add AIE4 work buffer initialization

NPU firmware requires a host-allocated work buffer for hardware contexts.
Allocate a 4 MB host buffer and attach it to device during device init.

Refactor aie2_alloc_msg_buffer() and aie2_free_msg_buffer() into common
helpers by moving them to aie.c and renaming them to
amdxdna_alloc_msg_buffer() and amdxdna_free_msg_buffer(), allowing both
AIE2 and AIE4 to reuse the implementation.

Signed-off-by: Nishad Saraf <nishads@amd.com>
Reviewed-by: Mario Limonciello (AMD) <superm1@kernel.org>
Signed-off-by: Lizhi Hou <lizhi.hou@amd.com>
Link: https://lore.kernel.org/all/20260505160936.3917732-7-lizhi.hou@amd.com/