soc/nordic/nr54l: increase flash erase time define

Time it takes to "erase" one "page" of rram is too low.
Where getting timeouts.
"erase" of rram is done by writing all the words.
one "page" is 4096 bytes meaning 1024 32bit words.
worstcase time it takes to write one 32bit word from
0x00000000 to 0xffffffff is about 42us, giving 42ms
to write 1024 words.

Signed-off-by: Martin Tverdal <martin.tverdal@nordicsemi.no>