avb: Make AVB independent of fastboot

avb: Make AVB independent of fastboot

AVB only uses CONFIG_FASTBOOT_BUF_ADDR from fastboot for memory.
This memory is used for assigning temporary buffers.
This can be assigned a new variable and used as CONFIG_AVB_BUF_ADDR.
This is to support future boards that support AVB but dont support
USB and therefore dont support FASTBOOT.

Signed-off-by: Usama Arif <[email protected]>
Cc: Igor Opaniuk <[email protected]>
Reviewed-by: Tom Rini <[email protected]>
Acked-by: Igor Opaniuk <[email protected]>
[trini: Change defaults]
Signed-off-by: Tom Rini <[email protected]>