drm/i915: use REG_BIT on FW_BLC_SELF_* macros

Use REG_BIT() instead of open coding the shift in the FW_BLC_SELF_*
macro definitions to avoid potentially typing them as 'int'.

For example, this happens when we pass them to _MASKED_BIT_ENABLE(),
because of the typeof() construct there. When we pass 1 << 15 (the
FW_BLC_SELF_EN macro), we get typeof(1 << 15), which is 'int'. Then
the value becomes negative (-2147450880) and we try to assign it to a
'u32'.

In practice this is not a problem though, because when we try to
assign -2147450880 to the u32, that becomes 0x80008000, which was the
intended result.

Link: https://lore.kernel.org/intel-gfx/[e-mail]/
Reviewed-by: Jani Nikula <[e-mail]>
Reviewed-by: Andi Shyti <[e-mail]>
Signed-off-by: Luca Coelho <[e-mail]>

drivers/gpu/drm/i915/i915_reg.h

···
 #define FW_BLC		_MMIO(0x20d8)
 #define FW_BLC2		_MMIO(0x20dc)
 #define FW_BLC_SELF	_MMIO(0x20e0) /* 915+ only */
-#define   FW_BLC_SELF_EN_MASK      (1 << 31)
-#define   FW_BLC_SELF_FIFO_MASK    (1 << 16) /* 945 only */
-#define   FW_BLC_SELF_EN           (1 << 15) /* 945 only */
+#define   FW_BLC_SELF_EN_MASK      REG_BIT(31)
+#define   FW_BLC_SELF_FIFO_MASK    REG_BIT(16) /* 945 only */
+#define   FW_BLC_SELF_EN           REG_BIT(15) /* 945 only */
 #define MM_BURST_LENGTH     0x00700000
 #define MM_FIFO_WATERMARK   0x0001F000
 #define LM_BURST_LENGTH     0x00000700