rge.4: fix incorrect speed range in HARDWARE section

The HARDWARE section stated "PCIe 1GB to 1GB Ethernet devices"
which is incorrect. The RTL8125/8126/8127 chips support speeds
from 1Gbps to 10Gbps. Correct the range.

Signed-off-by: Christos Longros <chris.longros@gmail.com>

rge.4: note that the driver manages PHY directly

The rge(4) driver does not use the miibus(4) interface for PHY
management. Instead, it accesses PHY registers directly via the
chip's OCP (On-Chip Peripheral) bus. Document this in the
DESCRIPTION section.

Signed-off-by: Christos Longros <chris.longros@gmail.com>

Reviewed by: adrian
Differential Revision: https://reviews.freebsd.org/D55995