perf: arm_spe: Fail device probe when arm64_kernel_unmapped_at_el0()

When running with the kernel unmapped whilst at EL0, the virtually-addressed
SPE buffer is also unmapped, which can lead to buffer faults if userspace
profiling is enabled and potentially also when writing back kernel samples
unless an expensive drain operation is performed on exception return.

For now, fail the SPE driver probe when arm64_kernel_unmapped_at_el0().

Reviewed-by: Mark Rutland <mark.rutland@arm.com>
Tested-by: Laura Abbott <labbott@redhat.com>
Tested-by: Shanker Donthineni <shankerd@codeaurora.org>
Signed-off-by: Will Deacon <will.deacon@arm.com>