pinctrl: bcm283x: Add GPIO pull-up/down control for BCM2835 and BCM2711

pinctrl: bcm283x: Add GPIO pull-up/down control for BCM2835 and BCM2711

This patch adds support for configuring GPIO pull-up and pull-down
resistors in the BCM283x pinctrl driver. It implements the brcm,pull
device tree property to control pin bias settings.

The implementation follows the hardware-specific pull control
mechanisms:
- BCM2835: two-step GPPUD register sequence
- BCM2711: direct per-pin control registers

This enables device tree configurations to specify pull-up, pull-down,
or no bias for individual GPIO pins.

Tested on Raspberry Pi boards with both BCM2835 and BCM2711 SoCs.

Signed-off-by: Cibil Pankiras <cibil.pankiras@egym.com>
Reviewed-by: Matthias Brugger <mbrugger@suse.com>