Squashed commit of the following:
arch/arm/src/samd5e5: Clean-up EIC logic.
arch/arm/src/samd5e5: Fix some compilation issues; Still issues with the EIC logic from samd2x.
arch/arm/src/samd5e5: Fix some compilation issues; bring in some EIC logic from samd2x.
arch/arm/src/samd5e5: Add NVMCTRL header file, fix some compiler problems, misc. clean-up.
configs/metro-m4: Add LED support.
arch/arm/src/samd5e5: Bring in SAML21 clock configuration. This is a WIP; it cannot possible even compile yet.
arch/arm/src/samd5e5: Leverage Cortex-M4 interrupt and SysTick logic from the SAM3/4.
arch/arm/src/samd5e5: Add SERCOM utility function.
arch/arm/src/samd5e5: Bring all SERCOM USART logic from SAMD2L2 to SAMD5E5. This is a brute coy with nothing more than more that name changes and extension from 5 to 7 SERCOMs.
arch/arm/src/samd5e5: Add sam_config.h header file
arch/arm/src/samd5e5/: Add Generic Clock (GCLK) utility functions.
arch/arm/src/samd5e5: Add EVSYS register definition file
arch/arm/src/samd5e5 and configs/metro-m4: Use SERCOM3 for the Arduino serial shield as console.
arch/arm/src/samd5e5/chip: Add SERCOM USART, SPI, I2C master, and slave register defintions header files
arch/arm/src/samd5e5/chip: Add AES, PM, TRNG, and WDT header files.
arch/arm/src/samd5e5/chip: Add pin multiplexing header files.
Various fixes to configuration system; fix metro-m4/nsh defconfig file.
configs/metro-m4: Add initial support for the Adafruit Metro M4 board.
arch/arm/src/samd5e5: Add peripheral clock helpers.
arch/arm/src/samd5e5/chip: Add PAC register definition header file. Fix some errors in the memory map header file.
arch/arm/src/samd5e5: Add chip.h headerf file.
arch/arm/src/samd5e5: Add PORT register definitions and support from SAML21.
arch/arm/include/samd5e5: Add interrupt vector definitions.
arch/arm/src/samd5e5: Add some boilerplate files. Correct some typos.
arch/arm/src/samd5e5/chip/sam_eic.h: Add EIC register definitions.
arch/arm/src/samd5e5/chip: Add OSC32KCTRL and OSCCTRL register definitions.
arch/arm/src/samd5e5/chip: Add GCLK, MCLK, and RSTC header files.
arch/arm/src/samd5e5/chip/sam_cmcc.h: Add CMCC register definitions
arch/arm/src/samd5e5/chip/sam_supc.h: Add SUPC header file.
arch/arm/src/samd5e5: Add start-up logic.
arch/arm/src/samd5e5: Add Make.defs file
arch/arm/src/samd5e5/chip: Add memory map header file.
arch/arm/include/samd5e5: Add chip.h header file.
arch/arm/Kconfig and arch/arm/src/samd5e5/Kconfig: Add configuration logic for the SAMD5x/Ex family.
