defconfig: arm64: Enable UART functionality for SDM855

UART functionality is used for console, and for clients such as BT.
This commit enables UART related functionalities for SDM855 to enable
High-Speed UART, and console UART.

CRs-Fixed: 2124301
Change-Id: I6729f1a8749d3f13267ed2c46af75726c443434d
Signed-off-by: Sagar Dharia <sdharia@codeaurora.org>