drm/arm: fix unintentional integer overflow on left shift

Shifting the integer value 1 is evaluated using 32-bit arithmetic
and then used in an expression that expects a long value leads to
a potential integer overflow. Fix this by using the BIT macro to
perform the shift to avoid the overflow.

Addresses-Coverity: ("Unintentional integer overflow")
Fixes: ad49f860

 ("drm/arm: Add support for Mali Display Processors")
Signed-off-by: Colin Ian King <colin.king@canonical.com>
Acked-by: Liviu Dudau <liviu.dudau@arm.com>
Signed-off-by: Liviu Dudau <Liviu.Dudau@arm.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20200618100400.11464-1-colin.king@canonical.com