r8152: Add helper functions for SRAM2

r8152: Add helper functions for SRAM2

Add the following helper functions for SRAM2 access to simplify the code
and improve readability:

- sram2_write() - write data to SRAM2 address
- sram2_read() - read data from SRAM2 address
- sram2_write_w0w1() - read-modify-write operation

Signed-off-by: Chih Kai Hsu <hsu.chih.kai@realtek.com>
Reviewed-by: Hayes Wang <hayeswang@realtek.com>
Link: https://patch.msgid.link/20260401115542.34601-1-nic_swsd@realtek.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>