clk: at91: Convert to common field_{get,prep}() helpers

clk: at91: Convert to common field_{get,prep}() helpers

Drop the driver-specific field_get() and field_prep() macros, in favor
of the globally available variants from <linux/bitfield.h>.

Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Acked-by: Alexandre Belloni <alexandre.belloni@bootlin.com>
Acked-by: Stephen Boyd <sboyd@kernel.org>
Acked-by: Claudiu Beznea <claudiu.beznea@tuxon.dev>
Signed-off-by: Yury Norov (NVIDIA) <yury.norov@gmail.com>