Ignore sparse warnings on restricted integer types

Add "-Wbitwise" flag to prevent sparse from treating "cast to restricted
__le32" warnings as errors. This warning originates from the kernel code
and is not a driver issue. In the kernel header(asm-generic/io.h), a
u32 type is implicitly cast to a restricted type "le32" and sparse
throws a warning. This doesn't affect the driver functionality and can
be ignored. Note that this issue exists only in kernel version from 6.0
to 6.2.x. In v5.x and v6.3.0 or later this issue is fixed.

Change-Id: Ibc6533a55678b0515b0ffe0af80128dc5293dde3
Signed-off-by: Rajasekaran Kalidoss <rajasekaran.kalidoss@arm.com>