hw: get rid of global makefiles specific to hw

This commit mostly removes the globally visible NR_OF_CPUS define
from the global makefile specifiers defined in the base-hw repository.
Whereever necessary it adds platform specific makefiles to the base
repository when they were missing.

Ref #2190

repos/base-hw/etc/specs.conf

@@ -0,0 +1,10 @@
+SPECS += genode hw
+
+ifeq ($(filter-out $(SPECS),x86_64),)
+SPECS += pci ps2 vesa framebuffer
+
+ifneq ($(filter-out $(SPECS),muen),)
+SPECS += acpi
+endif
+
+endif