phy: ti: am654: simplify regfield handling

regfield handling in current driver code is made complicated
by having a separate regfield variable for each field which
is allocated individually.

This quickly gets unwieldy once number of regfields increase.
Instead, use an array of regfields which are allocated in a
loop.

Signed-off-by: Sekhar Nori <nsekhar@ti.com>
Link: https://lore.kernel.org/r/20200727194603.44636-2-nsekhar@ti.com


Signed-off-by: Vinod Koul <vkoul@kernel.org>