Move per-transition delays from generic bit-bashing layer to i2c layer

(since SPI bit-bashing will require different delay semantics).

src/drivers/bitbash/bitbash.c

 void write_bit ( struct bit_basher *basher, unsigned int bit_id,
 		 unsigned long data ) {
 	basher->write ( basher, bit_id, ( data ? -1UL : 0 ) );
-	udelay ( basher->udelay );
 }
 
 /**

src/drivers/bitbash/i2c_bit.c

  * that provides two lines: SCL (clock) and SDA (data).
  */
 
+/**
+ * Delay between output state changes
+ *
+ * Max rated i2c speed (for the basic i2c protocol) is 100kbps,
+ * i.e. 200k clock transitions per second.
+ */
+static void i2c_delay ( void ) {
+	udelay ( I2C_UDELAY );
+}
+
 /**
  * Set state of I2C SCL line
  *
  * @v basher		Bit-bashing interface
  * @v state		New state of SCL
  */
-static inline __attribute__ (( always_inline )) void
-setscl ( struct bit_basher *basher, int state ) {
+static void setscl ( struct bit_basher *basher, int state ) {
 	write_bit ( basher, I2C_BIT_SCL, state );
+	i2c_delay();
 }
 
 /**
  * @v basher		Bit-bashing interface
  * @v state		New state of SDA
  */
-static inline __attribute__ (( always_inline )) void
-setsda ( struct bit_basher *basher, int state ) {
+static void setsda ( struct bit_basher *basher, int state ) {
 	write_bit ( basher, I2C_BIT_SDA, state );
+	i2c_delay();
 }
 
 /**
  * @v basher		Bit-bashing interface
  * @ret state		State of SDA
  */
-static inline __attribute__ (( always_inline )) int
-getsda ( struct bit_basher *basher ) {
+static int getsda ( struct bit_basher *basher ) {
 	return read_bit ( basher, I2C_BIT_SDA );
 }
 
 	assert ( basher->write != NULL );
 	i2cbit->i2c.read = i2c_bit_read;
 	i2cbit->i2c.write = i2c_bit_write;
-	basher->udelay = I2C_UDELAY;
 	i2c_stop ( basher );
 }

src/include/gpxe/bitbash.h

 	 * @ret non-zero	Input is a logic 1
 	 */
 	int ( * read ) ( struct bit_basher *basher, unsigned int bit_id );
-	/** Delay between subsequent calls to write(), in microseconds */
-	unsigned int udelay;
 };
 
 extern void write_bit ( struct bit_basher *basher, unsigned int bit_id,