uart: Replace Init calls with Enable/Disable

* Enable/Disable makes more sense and matches
  platform loader serial functions.
* Rework PL011 code after finding a PDF covering
  the details of it.
* Rename UART global defines in loader to be more
  exact about location

headers/private/kernel/arch/arm/uart_8250.h

@@ -37,6 +37,9 @@ public:
 	void					Init();
 	void					InitPort(uint32 baud);
 
+	void					Enable();
+	void					Disable();
+
 	int						PutChar(char c);
 	int						GetChar(bool wait);
 
@@ -47,6 +50,7 @@ private:
 	void					WriteUart(uint32 reg, unsigned char data);
 	unsigned char			ReadUart(uint32 reg);
 
+	bool					fUARTEnabled;
 	addr_t					fUARTBase;
 };
 

headers/private/kernel/arch/arm/uart_pl011.h

@@ -93,9 +93,11 @@ public:
 							~UartPL011();
 
 	void					InitEarly();
-	void					Init();
 	void					InitPort(uint32 baud);
 
+	void					Enable();
+	void					Disable();
+
 	int						PutChar(char c);
 	int						GetChar(bool wait);
 
@@ -106,6 +108,7 @@ private:
 	void					WriteUart(uint32 reg, unsigned char data);
 	unsigned char			ReadUart(uint32 reg);
 
+	bool					fUARTEnabled;
 	addr_t					fUARTBase;
 };