ACPI: Kconfig: Provide help text for the ACPI_PRMT option

Add missing help text for CONFIG_ACPI_PRMT.

Fixes: cefc7ca ("ACPI: PRM: implement OperationRegion handler for the PlatformRtMechanism subtype")
Reported-by: Borislav Petkov <bp@alien8.de>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

Author: rafaeljw

drivers/acpi/Kconfig

@@ -548,3 +548,13 @@ config ACPI_PRMT
 	bool "Platform Runtime Mechanism Support"
 	depends on EFI && X86_64
 	default y
+	help
+	  Platform Runtime Mechanism (PRM) is a firmware interface exposing a
+	  set of binary executables that can be called from the AML interpreter
+	  or directly from device drivers.
+
+	  Say Y to enable the AML interpreter to execute the PRM code.
+
+	  While this feature is optional in principle, leaving it out may
+	  substantially increase computational overhead related to the
+	  initialization of some server systems.