arm64: defconfig: Enable Qualcomm CPUCP mailbox driver

The Qualcomm CPUCP mailbox driver needs to be enabled for CPU frequency
scaling to work on the X Elite platform, so enable this driver.

Signed-off-by: Bjorn Andersson <bjorn.andersson@oss.qualcomm.com>
Reviewed-by: Konrad Dybcio <konrad.dybcio@oss.qualcomm.com>
Link: https://lore.kernel.org/r/20250605-enable-cpucp-v1-1-111ecef7e4c9@oss.qualcomm.com
Signed-off-by: Bjorn Andersson <andersson@kernel.org>