drivers/cpu: Add generic armv8 cpu driver

Add a generic driver that binds to armv8 CPU nodes. The generic driver allows
- to enumerate CPUs present in a system, even when no other driver binds it
- generates ACPI SSDT code for each CPU
- Fill the ACPI MADT table (implemented in a follow up patch)

The newly introduced code could also be reused on other CPU drivers that are
compatible with armv8.

TEST: Booted on QEMU sbsa and verify the driver binds to CPU nodes.
      Confirmed with FWTS that all ACPI processor devices are present.

Signed-off-by: Patrick Rudolph <patrick.rudolph@9elements.com>
Reviewed-by: Simon Glass <sjg@chromium.org>
Cc: Tom Rini <trini@konsulko.com>
Cc: Simon Glass <sjg@chromium.org>
diff --git a/drivers/cpu/Kconfig b/drivers/cpu/Kconfig
index 5c06cd9..9c0df33 100644
--- a/drivers/cpu/Kconfig
+++ b/drivers/cpu/Kconfig
@@ -26,6 +26,12 @@
 	help
 	  Support CPU cores for RISC-V architecture.
 
+config CPU_ARMV8
+	bool "Enable generic ARMv8 CPU driver"
+	depends on CPU && ARM64
+	help
+	  Support CPU cores for armv8 architecture.
+
 config CPU_MICROBLAZE
 	bool "Enable Microblaze CPU driver"
 	depends on CPU && MICROBLAZE