tee: optee: ffa: support shared memory offsets on large-page kernels

OP-TEE FF-A memory objects use 4 KiB pages, while the kernel page
size may be larger. Consequently, tee_shm->offset can be greater than
or equal to FFA_PAGE_SIZE, but OP-TEE rejects such a value in
internal_offs.

Do not encode the excess page offset in offs_low/offs_high. Those
fields describe the logical memref offset and are copied back into
tee_param->shm_offs on return. Folding the page offset into them breaks
parameter round trips when a memref is reused. They are also ignored by
the OPTEE_RPC_CMD_SHM_ALLOC response path, which uses only global_id and
internal_offs to construct the shared-memory mobj.

Instead, start the FF-A descriptor at the 4 KiB page containing the
shared buffer, the same approach as optee_fill_pages_list() in the SMC
ABI. Store the remaining in-page offset in internal_offs and preserve
shm_offs in offs_low/offs_high. This keeps internal_offs within the
FF-A page size, maps RPC allocations at the correct address, and
preserves normal memref offsets across repeated invocations.

Tested on ARMv8-A with 64 KiB PAGE_SIZE. OP-TEE OS ran as a secure
partition under Hafnium (SPMC) over FF-A. Verified registered shared
memory with tee_shm->offset >= 4 KiB, memref reuse on the same
TEEC_Operation, and RPC OPTEE_RPC_CMD_SHM_ALLOC (xtest regression
6007-6009). optee_hello_world, optee_aes, and xtest regression 1005,
1007, 1008, 4001-4003 and 6001-6003 also passed.

Fixes: 4615e5a34b95 ("optee: add FF-A support")
Acked-by: Liming Sun <limings@nvidia.com>
Acked-by: James Hurley <jahurley@nvidia.com>
Acked-by: Dave Thompson <davthompson@nvidia.com>
Signed-off-by: Mahantesh Salimath <mahantesh@nvidia.com>
Reviewed-by: Sumit Garg <sumit.garg@oss.qualcomm.com>
Signed-off-by: Jens Wiklander <jens.wiklander@oss.qualcomm.com>

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