uchcom: add support for CH9102 and CH343 uarts

The CH343 devices support any baud rate up to 6 Mbps.
PR: 272803
Reviewed by: imp
Tested by: joerg, Tomasz "CeDeROM" CEDRO <tomek_AT_cedro_DOT_info>
Differential Revision: https://reviews.freebsd.org/D46290

(cherry picked from commit 1395712cab8e95808064ba68c5a792b7cd0fe35f)