Nitrogen6x-lite: Replace i.MX6 Solo by i.MX6S

Use the same name convention for variable SOC used in other machines.
This mismatch was highlighted during the automatic generation of supported
machine list for FSL Community BSP Release Notes 1.7.

Signed-off-by: Daiane Angolini <daiane.angolini@freescale.com>
Acked-by: Eric Nelson <eric.nelson@boundarydevices.com>
Signed-off-by: Otavio Salvador <otavio@ossystems.com.br>
u-boot-*: Add DESCRIPTION for u-boot providers

Add u-boot DESCRIPTION for those providers still using the default one.
This is needed in order to have a complete and readable list of u-boot providers
in FSL Community BSP Release Notes.

Signed-off-by: Daiane Angolini <daiane.angolini@freescale.com>
Signed-off-by: Otavio Salvador <otavio@ossystems.com.br>