irqchip/irq-realtek-rtl: Add/simplify register helpers

irqchip/irq-realtek-rtl: Add/simplify register helpers

The Realtek interrupt controller has two important registers that are used
by the driver in several places

 - GIMR: global interrupt mask register
 - IRR: Interrupt routing registers

The usage of these registers is very inconsistent. GIMR is addressed
directly while IRR has a helper that needs a macro as an input. Harmonize
this by providing consistent helpers that improve code readability.

The callers of these helpers use classic lock/unlock functions and
sometimes use the wrong locking helper. E.g. irqsave variants are used in
mask/unmask although not needed. Adapt and fix the surrounding call
locations.

Signed-off-by: Markus Stockhausen <markus.stockhausen@gmx.de>
Signed-off-by: Thomas Gleixner <tglx@kernel.org>
Link: https://patch.msgid.link/20260604182506.1113440-2-markus.stockhausen@gmx.de