Introduce a CPU_V6K configuration option for platforms to select if they
have a V6K CPU core.  This allows us to identify whether we need to
support ARMv6 CPUs without the V6K SMP extensions at build time.

Currently CPU_V6K is just an alias for CPU_V6, and all places which
reference CPU_V6 are replaced by (CPU_V6 || CPU_V6K).

Select CPU_V6K from platforms which are known to be V6K-only.
Acked-by: NTony Lindgren <tony@atomide.com>
Tested-by: NSourav Poddar <sourav.poddar@ti.com>
Tested-by: NWill Deacon <will.deacon@arm.com>
Signed-off-by: NRussell King <rmk+kernel@arm.linux.org.uk>