BaseTools: Change the [Arch][Name] module key in Build cache

BaseTools: Change the [Arch][Name] module key in Build cache

BZ: https://bugzilla.tianocore.org/show_bug.cgi?id=1951

Current build cache use the module's [self.Arch][self.Name]
info as the ModuleAutoGen object key in hash list and dictionary.
The [self.Arch][self.Name] is not safe as the module key because
there could be two modules with same module name and arch name in
one platform. E.g. A platform can override a module or library
instance in another different path, the overriding module can has
the same module name and arch name as the original one.
Directly use the ModuleAutoGen obj self as the key, because
the obj __hash__ and __repr__ attributes already contain the
full path and arch name.

Cc: Liming Gao <liming.gao@intel.com>
Cc: Bob Feng <bob.c.feng@intel.com>
Signed-off-by: Steven Shi <steven.shi@intel.com>
Reviewed-by: Bob Feng <bob.c.feng@intel.com>