types.h: Add a helper macro BITS_PER_BYTE

This change adds a helper macro `BITS_PER_BYTE` so that it doesn't
have to be defined in multiple places.

Change-Id: Idc344047a5660791eaeb1ce8012910c11f6010ba
Signed-off-by: Furquan Shaikh <furquan@google.com>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/49736
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: EricR Lai <ericr_lai@compal.corp-partner.google.com>
Reviewed-by: Tim Wawrzynczak <twawrzynczak@chromium.org>

src/include/types.h

@@ -18,4 +18,6 @@
 #define BIT(x)				(1ul << (x))
 #endif
 
+#define BITS_PER_BYTE			8
+
 #endif /* __TYPES_H */