arm64: zynqmp: Remove PM firmware checking

Having zynqmp firmware is actually only one valid configuration. In QEMU
case for example there is no PMU that's why this checking can't end up in
panic that's why code remove this code completely.

Signed-off-by: Michal Simek <michal.simek@amd.com>
Link: https://lore.kernel.org/r/05b8bbf0686c72f86ea7f8bfe0da250ddba9e211.1722336162.git.michal.simek@amd.com