psu-ng: Change the GPIOReader class to GPIOInterface

The GPIOReader class only contains a read function. A new write function
will be added so it makes sense for the class to be named Interface
instead of Reader.
Change GPIOReader to GPIOInterface, and change the base class from
GPIOInterface to GPIOInterfaceBase.

Tested: Ran CI.

Change-Id: I2a4abdabe0136a7f73337f0d054d2dd79712f53c
Signed-off-by: Adriana Kobylak <anoo@us.ibm.com>
diff --git a/phosphor-power-supply/test/mock.hpp b/phosphor-power-supply/test/mock.hpp
index d494e14..d354c9f 100644
--- a/phosphor-power-supply/test/mock.hpp
+++ b/phosphor-power-supply/test/mock.hpp
@@ -50,7 +50,7 @@
                 (const, override));
 };
 
-class MockedGPIOReader : public GPIOInterface
+class MockedGPIOInterface : public GPIOInterfaceBase
 {
   public:
     MOCK_METHOD(int, read, (), (override));