cpufreq: maple: Remove maple driver

This driver is no longer buildable since the PPC_MAPLE platform was
removed, see commit 62f8f307 ("powerpc/64: Remove maple platform").

Remove the driver.

Note that the comment in the driver says it supports "SMU & 970FX
based G5 Macs", but that's not true, that comment was copied from
pmac64-cpufreq.c, which still exists and continues to support those
machines.

Acked-by: Viresh Kumar <viresh.kumar@linaro.org>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://patch.msgid.link/20241112085148.415574-1-mpe@ellerman.id.au