thermal: enable broadcom menu for arm64 bcm2835

Moving the bcm2835 thermal driver to the broadcom directory prevented it
from getting enabled for arm64 builds, since the broadcom directory is only
available when 32-bit specific ARCH_BCM is set.

Fix this by enabling the Broadcom menu for ARCH_BCM or ARCH_BCM2835.

Fixes: 6892cf07 ("thermal: bcm2835: move to the broadcom subdirectory")
Reviewed-by: Eric Anholt <eric@anholt.net>
Signed-off-by: Allen Wild <allenwild93@gmail.com>
Signed-off-by: Stefan Wahren <stefan.wahren@i2se.com>
Signed-off-by: Eduardo Valentin <edubezval@gmail.com>