boards: microchip: add SAM E54 Xplained Pro board support

Add initial support for the Microchip SAM E54 Xplained Pro board
(ATSAME54-XPRO).

Product page: https://www.microchip.com/en-us/development-tool/atsame54-xpro



Signed-off-by: Arunprasath P <arunprasath.p@microchip.com>