btrfs: add helper for bit enumeration
Define helper macro that can be used in enum {} to utilize the automatic
increment to define all bits without directly defining the values or
using additional linear bits.
1. capture the sequence value, N
2. use the value to define the given enum with N-th bit set
3. reset the sequence back to N
Use for enums that do not require fixed values for symbolic names (like
for on-disk structures):
enum {
ENUM_BIT(FIRST),
ENUM_BIT(SECOND),
ENUM_BIT(THIRD)
};
Where the values would be 0x1, 0x2 and 0x4.
Reviewed-by: Josef Bacik <josef@toxicpanda.com>
Signed-off-by: David Sterba <dsterba@suse.com>