acpi: Update default processor string from decimal to hex

Update the default processor sting from decimal to hex to increase
the default number of Processor NamedObjects from 100 to 256
ie: CP00-CP99 is now CP00-CPFF

This fixes MADT table generation for system up to 256 cores.

Signed-off-by: Marc Jones <marcjones@sysproconsulting.com>
Signed-off-by: Jonathan Zhang <jonzhang@meta.com>
Change-Id: Id60a39d99fa77d1d89ad655ddecdebcc8a422f74
Reviewed-on: https://review.coreboot.org/c/coreboot/+/69325
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Arthur Heymans <arthur@aheymans.xyz>
diff --git a/src/acpi/Kconfig b/src/acpi/Kconfig
index d1051d8..7afff4e 100644
--- a/src/acpi/Kconfig
+++ b/src/acpi/Kconfig
@@ -8,7 +8,7 @@
 
 config ACPI_CPU_STRING
 	string
-	default "\\_SB.CP%02d"
+	default "\\_SB.CP%02X"
 	depends on HAVE_ACPI_TABLES
 	help
 	  Sets the ACPI name string in the processor scope as written by