net: stmmac: qcom-ethqos: remove register field value obfuscations

Convert the register field values to something more human readable.

For example, using (BIT(29) | BIT(27)) to update a register field that
consists of bits 29:27 is an obfuscated way of writing decimal 5 for
this field. The comment above needs to explain that this value is 5.

Worse still is BIT(12) | GENMASK(9, 8), which is used to hide the
decimal value 19 for the bitfield 16:8.

Fix these, and a few others by using FIELD_PREP(). While it means we
have bare numeric constants, this is more preferable than having the
obfuscation.

Reviewed-by: Mohd Ayaan Anwar <mohd.anwar@oss.qualcomm.com>
Tested-by: Mohd Ayaan Anwar <mohd.anwar@oss.qualcomm.com>
Signed-off-by: Russell King (Oracle) <rmk+kernel@armlinux.org.uk>
Link: https://patch.msgid.link/E1vuSKa-0000000ASbo-2zQg@rmk-PC.armlinux.org.uk
Signed-off-by: Jakub Kicinski <kuba@kernel.org>