Use bitfield for EncCapability

[Timmmm]

Currently there's this code:

struct EncCapability = {
  perms      : bits(cap_uperms_width + cap_hperms_width),
  otype      : bits(cap_otype_width),
  reserved   : bits(cap_reserved_width),
  flags      : bits(cap_flags_width),
  internal_E : bit,
  T          : bits(cap_mantissa_width - 2),
  B          : bits(cap_mantissa_width),
  address    : bits(cap_addr_width)
}

function capBitsToEncCapability(c) : CapBits -> EncCapability = struct {
  perms      = c[127..112],
  reserved   = c[111..110],
  flags      = c[109..109],
  otype      = c[108..91],
  internal_E = c[90],
  T          = c[89..78],
  B          = c[77..64],
  address    = c[63..0]
}

I think Sail has a bitfield feature which is designed for this sort of thing.

bitfield EncCapability : bits(128) = {
  perms      : 127 .. 112,
  otype      : 111 .. 110, 
...