ASoC: core: Add component pin control functions

It's often the case that a codec driver will need to control its
own pins. However, if a name_prefix has been applied to this codec it
must be included in the name passed to any of the snd_soc_dapm_x_pin()
functions.

The behaviour of the existing pin control functions is reasonable, since
you may want to search for a fully-specified name within the scope of an
entire card. This means that we can't apply the prefix in these functions
because it will break card-scope searches.

Constructing a prefixed string "manually" in codec drivers leads to a lot
of repetition of the same code.

To make this tidier in codec drivers this patch adds a new set of
equivalent functions that take a struct snd_soc_component instead of a
dapm context and automatically add the component's name_prefix to the
given name. This makes it a simple change in codec drivers to be
prefix-safe.

The new functions are not quite trivial enough to be inlines and the
compiler won't be able to compile-away any part of them.

Although it looks somewhat inefficient to have to allocate a temporary
buffer and combine strings, the current design of the widget list
doesn't lend itself to a more optimized implementation - it's a single
list of all widgets on a card and is searched linearly for a matching
string. As pin state changes are generally low-frequency events it's
unlikely to be a significant issue - at least not enough to rewrite the
widget list handling just for this.

Signed-off-by: Richard Fitzgerald <rf@opensource.wolfsonmicro.com>
Signed-off-by: Mark Brown <broonie@kernel.org>