a6: enable device files

This is required for flashing A6 firmware.
a6: enable i2c read/write retries
WIP: test a6 simulate_error
defconfig: cleanup extra bt cfgs

Change-Id: I6f16cc8e86d512cd19df40cd8fe8da9cbcec79db
WIP: defconfig update + uhid fixes

Change-Id: I75dfe6cad28b0872745cb5db174a3ce23e40c3f5
defconfig: vpn cfgs

Change-Id: Iadb3fb5f0c47d8ed8e91196c2b715806ee6faeba
hsuart_tty: WIP-EXPERIMENTAL-WIP improve buffer mgmt