gpiostream: replace Resolution with Frequency

It's easier for people to think in term of frequency when working with bitstream
than with the clock cycle duration in µs.

experimental/devices/nrzled/nrzled.go

@@ -61,7 +61,7 @@ func New(p gpiostream.PinOut, numPixels int, f physic.Frequency, channels int) (
 		numPixels: numPixels,
 		channels:  channels,
 		b: gpiostream.BitStream{
-			Res: f.Duration(),
+			Freq: f,
 			// Each bit is encoded on 3 bits.
 			Bits: make([]byte, numPixels*3*channels),
 			LSBF: false,

experimental/devices/nrzled/nrzled_test.go

@@ -10,7 +10,6 @@ import (
 	"image/color"
 	"strconv"
 	"testing"
-	"time"
 
 	"periph.io/x/periph/conn/gpio/gpiostream"
 	"periph.io/x/periph/conn/gpio/gpiostream/gpiostreamtest"
@@ -57,7 +56,7 @@ func TestNew_3(t *testing.T) {
 					0x49, 0x24, 0x92, 0x49, 0x24, 0x92, 0x49, 0x24, 0x92, 0x49, 0x24, 0x92, 0x49, 0x24, 0x92, 0x49,
 					0x24, 0x92, 0x49, 0x24, 0x92, 0x49, 0x24, 0x92, 0x49, 0x24,
 				},
-				Res:  2500 * time.Nanosecond,
+				Freq: 400 * physic.KiloHertz,
 				LSBF: false,
 			},
 		},
@@ -105,7 +104,7 @@ func TestDraw_NRGBA_3(t *testing.T) {
 					0x6d, 0xb6, 0xdb, 0x6d, 0xb6, 0xdb, 0x6d, 0xb6, 0xdb, 0x6d, 0xb6, 0xdb, 0x6d, 0xb6, 0xdb, 0x6d,
 					0xb6, 0x92, 0x49, 0xb6, 0x92, 0x49, 0xb4, 0x92, 0x4d, 0x24,
 				},
-				Res:  2500 * time.Nanosecond,
+				Freq: 400 * physic.KiloHertz,
 				LSBF: false,
 			},
 		},
@@ -131,7 +130,7 @@ func TestDraw_RGBA_3(t *testing.T) {
 					0x6d, 0xb6, 0xdb, 0x6d, 0xb6, 0xdb, 0x6d, 0xb6, 0xdb, 0x6d, 0xa6, 0xdb, 0x6d, 0xa6, 0xdb, 0x6d,
 					0xa6, 0xda, 0x49, 0xb6, 0xd3, 0x4d, 0x34, 0xdb, 0x49, 0x36,
 				},
-				Res:  2500 * time.Nanosecond,
+				Freq: 400 * physic.KiloHertz,
 				LSBF: false,
 			},
 		},
@@ -159,7 +158,7 @@ func TestDraw_RGBA_4(t *testing.T) {
 					0xdb, 0x6d, 0xa6, 0xdb, 0x6d, 0xa6, 0xdb, 0x6d, 0xa6, 0xd2, 0x49, 0x24, 0xda, 0x49, 0xb6, 0xd3,
 					0x4d, 0x34, 0xdb, 0x49, 0x36, 0x92, 0x4d, 0x26,
 				},
-				Res:  2500 * time.Nanosecond,
+				Freq: 400 * physic.KiloHertz,
 				LSBF: false,
 			},
 		},
@@ -185,7 +184,7 @@ func TestDraw_Limits(t *testing.T) {
 					0x6d, 0xb6, 0xdb, 0x6d, 0xb6, 0xdb, 0x6d, 0xb6, 0xdb, 0x6d, 0xa6, 0xdb, 0x6d, 0xa6, 0xdb, 0x6d,
 					0xa6, 0xda, 0x49, 0xb6, 0xd3, 0x4d, 0x34, 0xdb, 0x49, 0x36,
 				},
-				Res:  2500 * time.Nanosecond,
+				Freq: 400 * physic.KiloHertz,
 				LSBF: false,
 			},
 		},
@@ -211,7 +210,7 @@ func TestWrite_3(t *testing.T) {
 					0x6d, 0xb6, 0xdb, 0x6d, 0xb6, 0xdb, 0x6d, 0xb6, 0x92, 0x49, 0xa4, 0x92, 0x49, 0x36, 0x92, 0x49,
 					0xa6, 0x92, 0x49, 0xb6, 0x92, 0x49, 0xb4, 0x92, 0x4d, 0x24,
 				},
-				Res:  2500 * time.Nanosecond,
+				Freq: 400 * physic.KiloHertz,
 				LSBF: false,
 			},
 		},