platform: generic: Use kconfig to set platform version and default name

The generic platform version and default name should be set based
on kconfig options so that users can override it.

Signed-off-by: Anup Patel <apatel@ventanamicro.com>
Reviewed-by: Andrew Jones <ajones@ventanamicro.com>
Tested-by: Andrew Jones <ajones@ventanamicro.com>
Acked-by: Atish Patra <atishp@rivosinc.com>
Tested-by: Atish Patra <atishp@rivosinc.com>