usb: sam0: Add support for SAME54

[benpicco]

The USB peripheral is the same as in previous SAM0 MCUs, but the clock setup is different.

split off from #14685

[zephyrbot]

All checks passed.

checkpatch (informational only, not a failure)

-:52: WARNING:SPACE_BEFORE_TAB: please, no space before tabs
#52: FILE: drivers/usb/device/usb_dc_sam0.c:181:
+#define SAM0_USB_IRQ_CONNECT(n) ^I^I^I^I\$

-:53: WARNING:SUSPECT_CODE_INDENT: suspect code indent for conditional statements (8, 8)
#53: FILE: drivers/usb/device/usb_dc_sam0.c:182:
+	do {							\
+	IRQ_CONNECT(DT_INST_0_ATMEL_SAM0_USB_IRQ_##n,		\

- total: 0 errors, 2 warnings, 100 lines checked

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[jfischer-no]

Please split it in three commits: changes for PAD? settings, changes for clock setup, and changes for IRQ connect and enable.

[benpicco]

Ok, I've split up the commit.