net/mlx5: Switch to more abstract scoped ksimd guard API on arm64

net/mlx5: Switch to more abstract scoped ksimd guard API on arm64

Instead of calling kernel_neon_begin/end directly, switch to the scoped
guard API which encapsulates those calls. This is needed because the
prototypes of those APIs are going to be modified and will require a
kernel mode FP/SIMD buffer to be provided, which the scoped guard API
will do transparently.

Cc: Saeed Mahameed <saeedm@nvidia.com>
Cc: Leon Romanovsky <leon@kernel.org>
Cc: Tariq Toukan <tariqt@nvidia.com>
Cc: Mark Bloch <mbloch@nvidia.com>
Reviewed-by: Jonathan Cameron <jonathan.cameron@huawei.com>
Acked-by: Catalin Marinas <catalin.marinas@arm.com>
Signed-off-by: Ard Biesheuvel <ardb@kernel.org>