drm/i915/reg: fix undefined behavior due to shift overflowing the constant

Use REG_GENMASK() and REG_FIELD_PREP() to avoid errors due to
-fsanitize=shift.

References: https://lore.kernel.org/r/20220405151517.29753-12-bp@alien8.de
Reported-by: Borislav Petkov <bp@suse.de>
Reported-by: Ruiqi GONG <gongruiqi1@huawei.com>
Cc: Randy Dunlap <rdunlap@infradead.org>
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20220518113315.1305027-1-jani.nikula@intel.com
(cherry picked from commit 230fb39f)